Rearranged UI slightly, bug fixes

- UI can now be resized down to around 650 x 350 px, rearranged several
buttons to allow that (fucked up listener code reorganizing courtesy of
the brilliant window builder...)
- Loading a big enough ship in small enough editor window would cause
the anchor to be placed at a negative position; added code preventing
that from happening
- Closing room properties window after selecting a different room will
now always redraw the correct room
- Fixed undo offset operation