mod cleanup

some grid state based checks to reduce the thruster iterations if they are not needed. Logic should remain unchanged, but we are going through thruster collection less often.

More robust natural gravity check to trigger defined planetary thrust limits

MassMultiplier hotfix, because of course I coded the multiplier in reverse :D

new MassMultiplier config variable (default 1.0) which is used to multiply the impact the mass has on the maximum cruising speed (less impact < 0 < more impact)

fixed non functional SpeedLimitsOnly config option, I removed it about 3 months back by mistake, but no one is most likely using it :D

added missing null check, didn't crash the script, but could cause unnecessary log errors