A bunch of random monster-related fixes

- Assassination targets *need* to re-run the init
  script after their aura is set, otherwise they won't
  actually have any proper shadow aura properties, and
  therefore won't be affected by time freeze.
- Stat changes caused by leveling up were causing
  monsters to self-destruct because their stats were
  being capped *after* being applied, making them
  reapply *again* and nuking their health bars.
- Monsters will only heal half of their health back
  when they level up.
- Friendly monsters set their master for tracking
  purposes, and friendlies only show their friend icon
  if they *have* a master, which they will if they're a
  summon.
- Monsters *physically cannot* go over level 1000, so
  make sure we cap that too.
Merge branch 'master' of https://github.com/Kyle873/DoomRPG