Need for propeller engine characteristics

[MarAlder]

We need additional parameters to describe propeller engines. Maybe as part of the engine performanceMap, but also open for other solutions.

Important are:

• shaft power (e.g., shaftPower, powerShaft; we maybe also need a dev-guide for this kind of naming conventions)
• propeller:
  • thrust (e.g., thrustPropeller, propellerThrust)
  • figure of merit
  • efficiency
  • rotational speed

And additional parameters might be discussed.