Make GtkScaleButton a widget that has a toggle button
as a child, just like all the other button widgets now.
The immediate benefit of this arrangement is to avoid
the "double focus" problem when we pop up the popup.
Update accessible, demos and tests to match.
The notebook grab_focus change in the previous commit made
backwards tabbing work as expected, and thereby changed the
output of one of the focus-chain tests.
The colorbutton contains a button which contains a colorswatch.
We want the focus to go straight to the button, nowhere else,
so mark the swatch as !can-focus.
Adapt tests to match.
Differentiate between wrapping around and
stopping at the end of the focus chain.
Update the existing tests, and add two
new ones where the difference matters.
Add a test that enumerates the focus chain by
emitting move-focus repeatedly, and compares
the result to expected output.
The test expects a ui file and a reference
file as input. The reference file can be created
using the --generate option.
