i.e. duplicate the buttons rather than change their content and have the same
handlers for both variants.  Hide the one we don't want at any given time and
use size-groups to get the same width regardless of the combination shown. All
so the ui doesn't jump around the place as the button content changes.

Change-Id: Icca938a6381da1feaf43fd11779d1d6d94d5d3a0