When labels in popups (typically headings) matched the name of a button,
the label would be activated instead of the button.
This caused the unwrap menu in the UV editor not to re-select "Unwrap"
when opening a second time.
Moves all `interface_region*` files to C++ except for the tooptip region
which is slightly more complicated. Also move a few other files as well.
This helps to simplify and speed up code, especially through the use
of better C++ data structures. This change builds on all platforms on
the buildbot.
