RCS block model switching, rescaling, fuel type selection.

Will replace the existing stand-alone RCS blocks. Should include an optional structural arm model(s) for additional part-count reduction.

Need some consideration on this -- may or may not be a good idea in the long run.

Module is written, needs testing / validation.
Should be able to be added to existing parts (and thus craft/vessels) without negative side-effects, but will need testing on that as well.
Configs need to be created for the models to be used as stand-offs; due to how the modular-rcs module works, these will likely need to be custom-defined models rather than re-using existing defs.

• Models need to conform to a standard of 1m diameter as seen by the module at scale = 1.
  • Any models that are not natively 1m in diameter will need to use the SUBMODEL feature to define pre-scaled model setups.
• The 'height' specification in the model def is used as the 'length' of the stand-off arm.
• The 'diameter' should always be 1m (fix your model scale using SUBMODEL)
• In the ModularRCS config, the 'standoffScale' should be the size of the mounting plate on the RCS port itself at scale = 1. E.g. If the back side of the RCS port is 0.2m across you should specify 0.2 as the 'standoffScale'.
• Supports texture set switching for the standoff model.