A Better Battle Master (and minor fighter chassis fixes)

[Sindeloke]

All right, I found a possible solution for Into the Fray. It's still a bit wonky because now it doesn't work mid-combat even if you've killed all the melee and are trying to close on the archers, but now it works for running away, so maybe it balances.

Also added a new OA ability to the fighter base class based on complaints made by the EK in an all-melee one-shot we ran this week.