Reworks all subsystem priorities to correspond with how the priority var is actually supposed to be used.
Relevant comment from MSO:
Prioritys are a weight that controls how much of the byond tick the subsystem will be allowed to have, 50 was the default, so a subsystem with a priority of 100 would be allocated twice the amount of runtime as normal, and 25 would get half the amount.
Also ports some minor MC micro-optimizations from TG.
4ca4332076