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)
* interpolators use providers for client/situations/parts/ground elevation
* interpolators do no longer use own situations/parts, but those from provider
* interpolators are no longer QObjects (as it is not needed)
* use gnd flag from situation for gnd interpolation, there is no longer a parts gnd flag interpolation
* guess parts during interpolation
* changed iterators to m_s[i] as it makes clearer which values are used
** the flag is transferred from parts -> situation in airspace monitor
** if the other client already provides and gnd.flag in situation this also works
* adjusted logging
* use providers in unit tests / adjusted tests
* improved situation verification/assert
