* helper method to detect disconnected state
* clear ATC info if disconnected or not available
* unit test for "finders"
* added Doxygen file
* formatting frequency in text message tabs
* Aircraft ICAO class: hasXX methods (hasAircraftCombinedType(), ..)
* Index Variant map, contains(index)
* Deleted context_network_textmessages.cpp and moved it into impl.cpp (this was only 1 method)
* Fixed bug refs#228