Disable selection coordinate text boxes when switching to irrelevant tools
All Image menu actions now remove the active selection

Previously, certain Image menu actions (Resize, Canvas Resize) would
attempt to preserve the current selection by resizing it to match.
While useful, this produces inconsistent behavior because the other
Image menu items simply remove the active selection.

Rather than have non-uniform behavior, I have changed it so that ALL
Image menu actions forcibly remove the active selection.  This creates
consistency, and with selections now being saved in the Undo/Redo stack,
it removes any potential for loss (because the user can simply Undo to
reclaim the previous selection and image size/orientation).