Optimizations, and ferram's first attempt at using github

Alright, this includes some optimization changes; most of them are pretty small, but it does reduce the overhead a tiny bit.

The new ModularFuelsPartModule is intended to handle any functions and variables that are needed by multiple PartModules; inherit from that instead of PartModule if a particular class needs that.  Currently, the MFPM class only handles the high-precision timestamping needed for volatile fuel boiloff and the refueling pump, but it can be expanded as needed.  As a side-effect of how it's currently set up, the MFPM causes all of this stuff to be done one frame later than in the original implementation in order to simplify handling fueling / boiloff due to persistence; this can be fixed but would require a large amount of recoding to ensure that all MFS fuel tanks are set up properly before OnStart is called (for the refueling pumps to work).

Also, hopefully I didn't botch my first attempt using github.