Separate client side build from SBT.
Clean .gitignore.
Merge branch 'master' into frontend-build

Conflicts:
	Gruntfile.js
Git hook was doing too much after Gruntfile refactor.
Merge branch 'master' into frontend-build

Conflicts:
	common/app/assets/AssetsPlugin.scala
	common/app/assets/images/global/sprite.png
	common/app/common/StaticAssets.scala
	common/app/conf/application.scala
	identity/conf/play.plugins
Merge branch 'master' into frontend-build

Conflicts:
	applications/conf/routes
	dev-build/conf/routes
	facia-dev-build/conf/routes
Merge pull request #1897 from guardian/frontend-build

Separate client side build from SBT.