Fixes entropy calculation

Fixed the entropy calculation so that it is easier to remove gas from a
hot gas mix, not harder. Added comments explaining the entropy
calculation. Also returns pump and filter efficiency to previous values.
Quick fix for engine core flow imbalance

A more thorough fix should probably involve providing a way for players
to control the flow rate.

Also tweaks emitters and allows collectors to be read using a multitool.
Allows power to be read by examining the collectors
Merge pull request #6171 from mwerezak/gas-entropy

Fixes gas entropy calculation + engine pump/injector flow imbalance issue