To do this, MENU and SUBMENU are split into two types (at last), and
a Widget type is introduced. This should allow lots of code to be
removed at some point.
It's a complete mess for now - many things are out of place or shown
when they shouldn't be - and we can't move around the game map. But,
it's a good start.
This commit implements loading and saving options from/to config, and
enough UI toolkit magic to allow changes to boolean options to be
persisted.
We now respect the "play movies" setting and take screen resolution
from the config file.
