This commit adds a feature in airspace monitor to store the history
of received aircraft parts. If needed the history can be retrieved
via context methods.
refs #835
In same step cleaned up contexts a bit
* added function for model set strings
* renamed functions to getModelSet... instead of installed models (the set is smaller and is what we want to use with DBus)
* signal when debug/log flags changed
* removed some \copydoc
* allow to enable/disable rev.lookup/matching messages
* removed reload model function (dangling)
