This adds a new button in the context bar so we have the three
available options to handle a transformation/drop pixels:
* Drop pixels and deselect (Esc key)
* Drop pixels but keep the selection (Enter key), new "Apply" command
* Discard changes/undo (Ctrl+Z)
This adds a new key context (Transformation) and also fixes tooltip
shortcuts on context bar buttons to show the current configured
shortcut for each action.
Reverts debab653fa and 194f8424a8
David Capello