[ZEPPELIN-1847] fix: Copy only html when html file changed
[ZEPPELIN-1847] fix: Copy only html when html file changed

### What is this PR for?

Reduce build time by avoiding to copy non-related files. Approx 3~4 secs as you can see below.

### What type of PR is it?
[Improvement]

### Todos

Nothing

### What is the Jira issue?

[ZEPPELIN-1847](https://issues.apache.org/jira/browse/ZEPPELIN-1847)

### How should this be tested?

1. `cd zeppelin-web`
2. `npm install` && `npm run start`
3. change any html file in `src/` and see log.
4. compare the result with master branch's

### Screenshots (if appropriate)

```
Running "watch" task
Waiting...
>> File "src/app/home/home.html" changed.

## before

Execution Time (2016-12-22 08:13:35 UTC)
loading tasks   130ms  ▇▇▇ 3%
htmlhint:src     84ms  ▇▇ 2%
newer:copy:dev   3.6s  ▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ 93%
Total 3.9s
Completed in 5.953s at Thu Dec 22 2016 17:13:39 GMT+0900 (KST) - Waiting…

## after

Execution Time (2016-12-22 08:14:27 UTC)
loading tasks       137ms  ▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ 52%
newer:htmlhint        3ms  ▇ 1%
newer:htmlhint:src   25ms  ▇▇▇▇▇▇▇ 10%
htmlhint:src         89ms  ▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ 34%
newer:copy:html       5ms  ▇▇ 2%
Total 261ms

Completed in 2.447s at Thu Dec 22 2016 17:14:27 GMT+0900 (KST) - Waiting…
```

### Questions:
* Does the licenses files need update? - NO
* Is there breaking changes for older versions? - NO
* Does this needs documentation? - NO

Author: 1ambda <1amb4a@gmail.com>

Closes #1791 from 1ambda/fix/DONT-copy-all-files-grunt and squashes the following commits:

30827e0 [1ambda] fix: Gruntfile.js lint errors
03e95f7 [1ambda] fix: Copy only html when html file changed

minahlee/incubator-zeppelin,astroshim/incubator-zeppelin,vrlo/zeppelin,pellmont/zeppelin,apache/incubator-zeppelin,Leemoonsoo/incubator-zeppelin,r-kamath/zeppelin,SarunasG/zeppelin-oidc,r-kamath/zeppelin,joroKr21/incubator-zeppelin,sravan-s/zeppelin,Nova-Boy/zeppelin,rconline/zeppelin,AlexanderShoshin/zeppelin,minahlee/incubator-zeppelin,rconline/zeppelin,raysteam/zeppelin,jongyoul/zeppelin,radicalbit/incubator-zeppelin,1ambda/zeppelin,IceKhan13/zeppelin,sctincman/zeppelin,SachinJanani/zeppelin,tzolov/incubator-zeppelin,datalayer/zeppelin,pellmont/zeppelin,sohaibiftikhar/zeppelin,VipinRathor/zeppelin,jongyoul/zeppelin,openthings/zeppelin,lresende/incubator-zeppelin,zetaris/zeppelin,SarunasG/zeppelin-oidc,1ambda/zeppelin,apache/zeppelin,YuanGunGun/zeppelin,hkropp/incubator-zeppelin,tzolov/incubator-zeppelin,jongyoul/incubator-zeppelin,wary/zeppelin,sravan-s/zeppelin,tinkoff-dwh/zeppelin,datalayer/zeppelin-datalayer,cfries/zeppelin,herval/zeppelin,sctincman/zeppelin,apache/zeppelin,VipinRathor/zeppelin,yu74n/zeppelin,tzolov/incubator-zeppelin,benoyantony/zeppelin,soralee/zeppelin,namanmishra91/zeppelin,radicalbit/incubator-zeppelin,YuanGunGun/zeppelin,cquptEthan/incubator-zeppelin,yorek/zeppelin,yu74n/zeppelin,herval/zeppelin,karuppayya/zeppelin,vipul1409/zeppelin,fogbeam/zeppelin_mirror,soralee/zeppelin,cfries/zeppelin,r-kamath/incubator-zeppelin,cfries/zeppelin,radicalbit/incubator-zeppelin,vipul1409/zeppelin,sergeymazin/zeppelin,raysteam/zeppelin,vrlo/zeppelin,hkropp/incubator-zeppelin,sctincman/zeppelin,r-kamath/zeppelin,zjffdu/zeppelin,sravan-s/zeppelin,sergeymazin/zeppelin,zjffdu/zeppelin,YuanGunGun/zeppelin,hkropp/incubator-zeppelin,pellmont/zeppelin,IceKhan13/zeppelin,raysteam/zeppelin,r-kamath/incubator-zeppelin,chilang/zeppelin,anthonycorbacho/incubator-zeppelin,benoyantony/zeppelin,AlexanderShoshin/zeppelin,anthonycorbacho/incubator-zeppelin,chilang/zeppelin,tinkoff-dwh/zeppelin,apache/incubator-zeppelin,hkropp/incubator-zeppelin,astroshim/zeppelin,zetaris/zeppelin,Leemoonsoo/zeppelin,herval/zeppelin,lresende/incubator-zeppelin,volumeint/zeppelin,tzolov/incubator-zeppelin,r-kamath/zeppelin,cfries/zeppelin,apache/incubator-zeppelin,fogbeam/zeppelin_mirror,prabhjyotsingh/zeppelin,Leemoonsoo/zeppelin,datalayer/zeppelin,yu74n/zeppelin,sergeymazin/zeppelin,cquptEthan/incubator-zeppelin,lresende/incubator-zeppelin,pellmont/zeppelin,Leemoonsoo/zeppelin,doanduyhai/incubator-zeppelin,hkropp/incubator-zeppelin,astroshim/zeppelin,vrlo/zeppelin,minahlee/zeppelin,yu74n/zeppelin,benoyantony/zeppelin,r-kamath/incubator-zeppelin,apache/zeppelin,apache/incubator-zeppelin,jongyoul/incubator-zeppelin,lresende/incubator-zeppelin,IceKhan13/zeppelin,yorek/zeppelin,cfries/zeppelin,YuanGunGun/zeppelin,benoyantony/zeppelin,jongyoul/incubator-zeppelin,vrlo/zeppelin,fogbeam/zeppelin_mirror,SarunasG/zeppelin-oidc,openthings/zeppelin,volumeint/zeppelin,tinkoff-dwh/zeppelin,yorek/zeppelin,tinkoff-dwh/zeppelin,jongyoul/zeppelin,IceKhan13/zeppelin,IceKhan13/zeppelin,hammertank/zeppelin,jongyoul/zeppelin,YuanGunGun/zeppelin,pellmont/zeppelin,Leemoonsoo/zeppelin,minahlee/zeppelin,radicalbit/incubator-zeppelin,prabhjyotsingh/incubator-zeppelin,SarunasG/zeppelin-oidc,prabhjyotsingh/zeppelin,mwkang/zeppelin,1ambda/zeppelin,prabhjyotsingh/zeppelin,openthings/zeppelin,SachinJanani/zeppelin,cquptEthan/incubator-zeppelin,minahlee/zeppelin,cquptEthan/incubator-zeppelin,chilang/zeppelin,prabhjyotsingh/incubator-zeppelin,jongyoul/incubator-zeppelin,sravan-s/zeppelin,tinkoff-dwh/zeppelin,zjffdu/zeppelin,joroKr21/incubator-zeppelin,hammertank/zeppelin,doanduyhai/incubator-zeppelin,hammertank/zeppelin,r-kamath/incubator-zeppelin,cfries/zeppelin,YuanGunGun/zeppelin,soralee/zeppelin,joroKr21/incubator-zeppelin,prabhjyotsingh/incubator-zeppelin,volumeint/zeppelin,anthonycorbacho/incubator-zeppelin,mwkang/zeppelin,fogbeam/zeppelin_mirror,joroKr21/incubator-zeppelin,sravan-s/zeppelin,datalayer/zeppelin,IceKhan13/zeppelin,yu74n/zeppelin,jongyoul/zeppelin,apache/zeppelin,minahlee/incubator-zeppelin,pravin-dsilva/zeppelin,IceKhan13/zeppelin,VipinRathor/zeppelin,mwkang/zeppelin,datalayer/zeppelin,wary/zeppelin,datalayer/zeppelin-datalayer,sctincman/zeppelin,r-kamath/incubator-zeppelin,hammertank/zeppelin,yorek/zeppelin,anthonycorbacho/incubator-zeppelin,hammertank/zeppelin,Nova-Boy/zeppelin,wary/zeppelin,rconline/zeppelin,sctincman/zeppelin,VipinRathor/zeppelin,tinkoff-dwh/zeppelin,zetaris/zeppelin,anthonycorbacho/incubator-zeppelin,openthings/zeppelin,sohaibiftikhar/zeppelin,joroKr21/incubator-zeppelin,zjffdu/zeppelin,sctincman/zeppelin,herval/zeppelin,Leemoonsoo/zeppelin,prabhjyotsingh/zeppelin,doanduyhai/incubator-zeppelin,sohaibiftikhar/zeppelin,pravin-dsilva/zeppelin,prabhjyotsingh/zeppelin,sctincman/zeppelin,SachinJanani/zeppelin,chilang/zeppelin,astroshim/incubator-zeppelin,yorek/zeppelin,VipinRathor/zeppelin,minahlee/zeppelin,VipinRathor/zeppelin,hammertank/zeppelin,sohaibiftikhar/zeppelin,vrlo/zeppelin,openthings/zeppelin,namanmishra91/zeppelin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