SSTU - Shadow Space Technologies Unlimited

* FIX - ModularPart losing customized settings whenever the 'variant' was not the default. #730
* FIX - PartUpgrades for ModularFuelTank 'tank types' being missing / unresearchable in career mode. #731
* FIX - DP0-P/DP1-P now have drogue chutes added to them; should alleviate issues of 'unsafe' speeds resulting in loss of mission when the chute refused to open. #644
* CHANGE - Minor update to the SSTU-ENG-F1 PBR textures -- clean up a visible seam in NRM map, adjust colors on exhaust manifold, add quick 'dirt' layer generator.