Fix transform bugs

* Fixes creature powers being saved to the save file.
* Fixes temporary transformations being saved as if they were permanent.
* Fixes a crash caused by trying to copy Effects between the player and the
transformed creature. This involved adding an overloaded '=' operator to
EffectManager and executing clearEffects() when transforming. This means that
hero effects aren't saved for when they untransform.
* Fixes item bonuses to base stats (Phys/Ment/Off/Def) not being applied when
untransforming.