Don't use $rootScope.currentMainCategory

Use CategoryService._selectedCategories instead.
Use CategoryService._allCategories not $rootScope.categories.
Rename ForumNavBarController to CategoryController.
Use Gulp not Grunt ini Makefile, rename from 'grunt' to 'gulp'.
Fix Gulp script bug.
Avoid unnecessary Scala code recompilation.
Merge branch 'topic-faster-builds' into topic-angularjs-forum.
List topics also for the index state.
Load recent topics from database.