Give only available weapons in CA/FT/LMS v2

This replaces !631 (closed) and this branch includes !677 (merged) (though not much of it is left intact).

The defaults are to only give available in FT and LMS for now to test it out but keep current behavior in CA for now. Also whitelisting as BADCVARS to let admins test.

Also did some cleanup along the way. The warmup_stage checks should not be necessary since it only sets the cvars, every time they're actually read they're behind an if so warmup values only take effect during warmup. Some mutators already set warmup start weapons without a condition.