Fenu now holds the image, and update is invoke from the fenu itself.
After button deleted, it shows the predecessor's button. (If it was once covered.)
Implement dirty check.
Merge remote-tracking branch 'upstream/master'
Fix dirty not set when create, paste, delete button
Dummy save.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Fenubars/Display/Fenu.cs