* fixed isCurrentThreadCreatingThread and renamed to isCurrentThreadObjectThread (this check was never working), added 2 more thread checks
* changed remove aircraft function to return number of returned aircraft (like with the containers this allows to avoid unnecessary signals)
* removed unused function ps_recalculateRenderedAircraft() / SimulatorCommon
* using Queued airspaceAircraftSnapshot signal for binding (functor connect does not provide connection type)
* extened ASSERTs to check threads
* simulator: initial situation function with return value (success?)
* simulator: avoid unneccessary copy and provide correct rendered flag in add aircraft function
* added unload function to disconnect signals / slots and simulator
* changed remote provider to return signal/slot connections to manually disconnect functor connects
* flag so pause can freeze or continue AI aircraft
* slightly changed unload behaviour in simulator context
Remark: Tested for FSX only
Solves #424 for FSX
* missing exports for new classes
* public non virtual convertToQString, propertyByIndex
* removed left-over of watchdog
* virtual destructor for avionicsbase.h
* access via provider, access now possible also beyond the scope of interpolator
* will be used in (to be written airpace analyzer)
* renamed some member functions as required
* fixed some asserts / Doxygen comments
* adjusted unit tests
* added vtolAircraft flag for interpolator, not fully used everywhere
remarks: update signals for parts / situation still only needed in XP driver
