Added favorites feature to the files app

apps/files/appinfo/application.php

apps/files/appinfo/routes.php

apps/files/controller/apicontroller.php

apps/files/css/files.css

apps/files/index.php

apps/files/js/app.js

apps/files/js/favoritesfilelist.js

apps/files/js/favoritesplugin.js

apps/files/js/tagsplugin.js

apps/files/lib/helper.php

apps/files/service/tagservice.php

apps/files/simplelist.php

apps/files/templates/simplelist.php

apps/files/tests/js/favoritesfilelistspec.js

apps/files/tests/js/favoritespluginspec.js

apps/files/tests/js/tagspluginspec.js

apps/files/tests/service/tagservice.php

core/js/js.js