ModuleSystemHeatHarvester is slow #167

Most of this is in the stock implementations, so anything that we improve here should probably also be lifted into KSPCF patches.

Notable problems:

• PrepareRecipe gets called twice per FixedUpdate and makes a raycast each time.
• GetAbundance is the same for every single drill on the same vessel and should be cached.
• systemEfficiency doesn't actually do anything, because its changes to inputList and outputList get overridden by PrepareRecipe
• Inactive module instances still get FixedUpdate called every frame even when they aren't actually doing any work.