Rational: Except for FS9 we interpolate all aircraft in one loop at the same time. This can cause that some steps are always done at the same time for all aircraft of that loop. By passing the number we can more equally distribute such tasks, avoiding peaks.
* return interpolation results parts/situation in one step
* base class init for each interpolation step, less redundant code
* removed old interpolation/parts function
* adjusted unit tests and simulator objects (such as SimObject)
* no longer using the add parts/situations signals
* will use the remote aircraft provider parts directly
Result: all parts/situations are stored only once in memory and in one single place
