tests: Use `saveload` in more tests
Import order
`world` instead of `world.session.world`
Add two assertions

If we ever reach this, crashing is a good idea.
Line length, whitespace, comment and docstring fixes
Settings: Bold font for hotkey button labels (if defined)

Do not use "minus" for showing unassigned keys - empty buttons are
better - and do not imply anything about MINUS key.
Remove two kinds of files from release tarball (if present)

There's precedence for both accidentally ending up in a tarball.