Fixes for Arceus typing
Fix Arceus overriding Trick-or-Treat and Forest´s Curse.
Implement Arceus typing more reliably by setting it when it switches into the field.
Display fail messages when trying to modify Arceus´ first type by any means.
Also fix mons keeping their typing when changing to another forme.
Improve the fix to forme change
Merge pull request #613 from Slayer95/arceus

Fixes for Arceus typing