feat(theme): allow global disable of theming generation
feat(theme): allow global disable of theming generation

Support config-time disabling of Theming which in turn prevents
dynamic theme css generation and stylesheet injections.

```js
angular
   .module('myApp',['ngMaterial'])
   .config(['$mdThemingProvider', function($mdThemingProvider ){
      $mdThemingProvider.disableTheming();
   }]);
```

Refs #943. Closes #7959.

colinskow/material,bluebirdtech/material,acoreyj/material,ilovett/material,graingert/material,daniel-nagy/material,Frank3K/material,programmist/material,HarrisCorp/material,david-gang/material,miguelcobain/material,Splaktar/material,gkalpak/material,angular/material,j3ski/material,welkinhealth/material,pwistbac/material,dmitriz/material,imjoeco/material,oostmeijer/material,ServiceManagementGroup/material,ilovett/material,miguelcobain/material,epelc/material,DevVersion/material,crisbeto/material,ServiceManagementGroup/material,oostmeijer/material,programmist/material,vertazzar/material,bluebirdtech/material,Frank3K/material,Frank3K/material,hodeyp/material,crisbeto/material,DevVersion/material,SamDLT/material,pwistbac/material,DevVersion/material,j3ski/material,clshortfuse/material,Splaktar/material,david-gang/material,imjoeco/material,bluebirdtech/material,clshortfuse/material,hayloft/material,HarrisCorp/material,hayloft/material,j3ski/material,ilovett/material,hayloft/material,ErinCoughlan/material,marekmicek/material,dmitriz/material,colinskow/material,marekmicek/material,Splaktar/material,daniel-nagy/material,vertazzar/material,ErinCoughlan/material,dmitriz/material,daniel-nagy/material,epelc/material,SamDLT/material,angular/material,j3ski/material,acoreyj/material,vertazzar/material,HipsterZipster/material,colinskow/material,profoundry-us/material,HipsterZipster/material,hodeyp/material,SamDLT/material,angular/material,oostmeijer/material,welkinhealth/material,ServiceManagementGroup/material,graingert/material,miguelcobain/material,welkinhealth/material,miguelcobain/material,imjoeco/material,marekmicek/material,pwistbac/material,hodeyp/material,profoundry-us/material,graingert/material,angular/material,HipsterZipster/material,daniel-nagy/material,bluebirdtech/material,epelc/material,pwistbac/material,HipsterZipster/material,ErinCoughlan/material,ServiceManagementGroup/material,HarrisCorp/material,hayloft/material,epelc/material,david-gang/material,oostmeijer/material,graingert/material,DevVersion/material,HarrisCorp/material,marekmicek/material,profoundry-us/material,acoreyj/material,welkinhealth/material,crisbeto/material,clshortfuse/material,ErinCoughlan/material,Splaktar/material,hodeyp/material,dmitriz/material,crisbeto/material,gkalpak/material,colinskow/material,SamDLT/material,profoundry-us/material,Frank3K/material,acoreyj/material,imjoeco/material,programmist/material,ilovett/material,david-gang/material,gkalpak/material,gkalpak/material,programmist/material,vertazzar/material,clshortfuse/material