General clean up and finishing of SSTUHeatShield module, including new modes, and general improvement of functionality.

TODO:

• Add support for thermal soak type setups (e.g. insulative tiles). See the post by DR dev regarding his patch, and apply similar constraints using the directional effectiveness vector.
  • Will require a second code path for non-ablative shielding.
  • Active thermal soak shielding may be able to use the new 'core heat' mechanics introduced, as it appears those functions are implemented to automatically transfer heat towards radiators on the vessel.