Statblock refactoring

See #446 

Not much has changed externally, but here's what I feel is worth mentioning:

* Some of the key names in `engine/stats.txt` have changed. I'll submit a PR to flare-game with these changes.
* Tooltips in MenuCharacter's stat list have been changed to allow showing arbitrary bonuses to stats per level, per physical, etc.
* Transforming only copies stats in the `starting[]` array. I have tested transforming with flare-game's Stealth power, and everything seems to work as expected. However, there's always the chance that there are unintended consequences.