Cleaning up after gtk-builder-convert

I switched Slugathon from libglade to gtk.Builder back in August, using gtk-builder-convert on the XML files, then a few small boillerplate API changes in the Python code.

Just noticed today that a few dialogs weren't working correctly anymore. (This is the problem with waiting until something is "done" to actually release it — you have to find all the bugs yourself.)

The differences introduced were missing action-widget tags for some buttons, and changes in the ordering of the children within the dialog ActionArea.

Once I figured out what had happened, it was trivial to fix things up. But be sure to test all your dialogs after running gtk-builder-convert. Slugathon has unit tests, but they don't cover the user interface, so I didn't notice the bugs until I played a long test game to verify other changes.