fix drag and drop reordering when editing a header cell

[DivineDominion]

Just noticed that when you edit a header cell and then, while the field editor is still active, drag another cell in its place, I notice these things happen:

1. The dragged cell i drawn on top, okay

2. The edited cell is moved left or right to an adjacent column and draws itself with a background color in dark gray. It'd be better if the background color changed to default (white) when the column is being pushed away, even when its header cell is being edited. See:

   

3. The field editor stays where it was when you drop the new column under it. You can continue typing (better endEditing when dragging starts), which is super weird. See: