Added `featureImgDragDrop` alpha labs flag
Added `featureImgDragDrop` alpha labs flag

refs https://github.com/TryGhost/Team/issues/884

- used by Admin whilst working on drag/drop support and design

TryGhost/Ghost,janvt/Ghost,ErisDS/Ghost,ErisDS/Ghost,TryGhost/Ghost,ErisDS/Ghost,e10/Ghost,e10/Ghost,TryGhost/Ghost,janvt/Ghost