Update ve -> OO
Refactor how drag and drop is bound to the window frame
Merge pull request #2412 from Wikia/ve-fix-drag-and-drop

Refactor how drag and drop is bound to the window frame
VE-557: move widget styles into ve.ui.Widget; update class names (ve.ui -> oo.ui).
Merge branch 've-sprint-9' into VE-557