Added high grade fuels

Fuel is not required for most engines.  When used, fuel will boost engine torque (and consequently power) by 25%.  Making a tank active, and putting it on refuel duty will cause the tank to supply fuel to other nearby tanks.  Fuel consumption is based on engine type and engine power.  RPM and throttle also affect fuel consumption.  Diesels and turbines are efficient, while wankels and radials are not.

Also added electric motors without integrated batteries, which are lighter and take up less space, but require batteries to be supplied.