Separate settings options for health, magicka, and stamina grouping

[ceejbot]

Let's split these three potion categories out into their own settings so people who never chug magicka can ignore it. This is only a settings change, AFAICT-- three new settings, awareness of the three settings in the settings application bottleneck, etc. The mechanics of showing & applying won't need to change at all.

Oh wow, got the modularity right.