Kept on working on status effects.

- While on it, I streamlined a bit the API about status effects between game modes
  by using same-named API.
- I also removed the use of pointers where references would suffice,
  and removed the battle actor pointer copy in each battle status effects.
- Due to recent progress, I was able to add menu scripted actions for the First Aid
  and Shield spells + and thus added support for a boolean return values while on it.

What's left is to display stats effects in the party menu, and to load/save
the active status effects in save games.