Sharing of cells between dragged and displayed tabs

[monyschuk]

Currently, dragged tabs share the displayed tab's associated cell in order to fix an issue where, if the cell is copied, then text appears to be placed lower in the dragged tab than in the original tab.

While fixing LIGridControl's dynamic menu support, I noticed that failing to assign a menu to tabs (since they're dynamic) caused this same change in vertical text positioning. We may be able to revert to cell copies if we assign an empty menu to the copy where the original contains a menu, or if we adjust text y-offset in the cell based on the existence of an associated menu.