Implement importing .eng/.res files for motor data

[KoffeinFlummi]

Add the ability to import eng-files (RASP) into the motor struct.
Example: https://www.thrustcurve.org/simfiles/5f4294d20002e90000000673/
Should import motor name, total mass, propellant mass, empty mass, burn time as well as all the thrust/time data points.

Also add flag indicating if mass data is present or not