no app-level overrides are needed now.
1. on Windows, the windows buttons now behave and are drawn
just like all other apps -- proper bg coloring on hover and down,
and the right sizing.
2. and for the caption label, it is centered properly (by accounting
for the size of the windows_buttons button set), and then when the
window is too narrow, it is left-aligned in the remaining space
to ensure that it stil looks good.
