add btn-app color variations demo (#2903)
add btn-app color variations demo (#2903)


slachiewicz/AdminLTE,almasaeed2010/AdminLTE,slachiewicz/AdminLTE,garrettwong/AdminLTE,oyjt/AdminLTE,almasaeed2010/AdminLTE,garrettwong/AdminLTE,oyjt/AdminLTE,oyjt/AdminLTE