Add JSHint to our build.
Add JSHint to our build.

Right now it does not break the build when JSHint fails.
Will fix the errors in a separate review.

Testing Done:
./gradlew clean build works.

Bugs closed: AURORA-228

Reviewed at https://reviews.apache.org/r/21407/

shahankhatch/aurora,shahankhatch/aurora,protochron/aurora,apache/aurora,kidaa/aurora,apache/aurora,apache/aurora,wfarner/aurora,protochron/aurora,rdelval/aurora,rdelval/aurora,mschenck/aurora,thinker0/aurora,mschenck/aurora,kidaa/aurora,rdelval/aurora,mschenck/aurora,shahankhatch/aurora,crashlytics/aurora,crashlytics/aurora,medallia/aurora,medallia/aurora,rdelval/aurora,rdelval/aurora,mkhutornenko/incubator-aurora,rosmo/aurora,mkhutornenko/incubator-aurora,mkhutornenko/incubator-aurora,thinker0/aurora,crashlytics/aurora,wfarner/aurora,mschenck/aurora,shahankhatch/aurora,apache/aurora,apache/aurora,medallia/aurora,thinker0/aurora,kidaa/aurora,medallia/aurora,mschenck/aurora,wfarner/aurora,shahankhatch/aurora,thinker0/aurora,thinker0/aurora,wfarner/aurora,rdelval/aurora,kidaa/aurora,kidaa/aurora,rosmo/aurora,crashlytics/aurora,mkhutornenko/incubator-aurora,shahankhatch/aurora,protochron/aurora,apache/aurora,crashlytics/aurora,rosmo/aurora,rosmo/aurora,wfarner/aurora,protochron/aurora,rosmo/aurora,protochron/aurora,protochron/aurora,medallia/aurora,medallia/aurora,kidaa/aurora,mschenck/aurora,thinker0/aurora,mkhutornenko/incubator-aurora,crashlytics/aurora,wfarner/aurora,rosmo/aurora