Fix default alignment in MWImageModel

Make default alignment a computed value, and make sure the GUI listens
to 'choose' instead of 'select' events for SelectWidgets so to prevent
recursive calls and make sure the GUI is updated properly.

Also added a default alignment check on type change so the user can
visually have an indication that the new image will have a different
alignment. The user can then change the value manually.

Bug: 65564
Bug: 65596
Bug: 62852
Bug: 65617

Change-Id: I55e16775d18e0a4bf7f1fa73bbb3aa5e0aa51a79