Cleanup motors

motors.mat currently has multiple fields that are not used / not available. Motor should be re-organized to be more versatile.

First steps include:

• Avoid overshortening variable names (mFus, mc, ...; change them with more meaningful names, e.g: t -> time, T -> thrust ...)
• Use camelCase for variables: Ltank -> tankLength
• Merge Ixx, Iyy, Izz into inertia (3xn)
• Remove LastChange, mFus