More scale tweaks

[arbsoup]

While this is being reworked I figured I'd share some of my own install's custom changes to exponents in SystemHeat and CryoTanks. Namely:

• Removed the CoolingCost scaling for CryoTanks because (for the past couple years, and definitely in the newest version) this is a rate per unit mass of fuel so the overall cooling cost already scales.
• Gave SystemHeat harvesters and converters waste heat proportional to TweakScale's normal scaling for processing rate (exponent 3). That is, same amount of waste heat per resource extracted/converted.
• ModuleSystemHeatEngine has systemPower = 2.5 so waste heat scales with thrust (and fuel consumption etc.)
• Same for ModuleSystemHeatFissionEngine, though nothing seems to use systemPower so I applied it to HeatGeneration too.