add PC actor properties for `maxHealth` and `maxSpirit`

[rsek]

there's a few "canonical" mechanical items that modify maximum health/spirit, like Ironsworn's Battle-Scarred and Honourbound assets:

there's a logic to being able to set the Supply maximum as well - if only for the sake of symmetry - but that's complicated by the shared Supply option. maybe it could work if it's in System Config? on the other hand: no "canonical" assets alter Supply, and i've never spotted a homebrew asset that uses it. i'd be fine leaving Supply out of the initial implementation, and revisting it if demonstrates a need for it (e.g. specifically asks for it).

as far as exposing them to the player, adding that functionality to the PC sheet's meters in edit mode seems like a good bet. making them only adjust the maximum in edit mode might have the fringe benefit of telegraphing that edit mode is on, which some folks seem to miss.

[ben]

Looks like this would be addressed by whatever comes of #432.