Due to shallow-copy hackery, gui objects are not initialized on checkpoint load. This hacks around that by retargeting them. :|
- This is so, so not the clean design I had in mind. Will work on finding a more appropriate mode of operation. Perhaps just calling remove_object on each gui component before we add them?
- The reset code for the boss hp bar only works -once-. Don't die more than once for now.
- Probably won't crash.
Made boss_progress_display strict.

Graceful as _heck_.