* set sort order automatically to IndexOrder when changing order of items
* call onChanged when model is changed and then update view (needed when model is changed directly, not via view)
* support for digest signal so redundant updates can be avoided
* renamed rowCountChanged (signal) to modelDataChanged - detecting row count changes only was useless
* updated Doxygen / fixed typos
* discussion: https://dev.vatsim-germany.org/boards/22/topics/2027?r=2040#message-2040
* fixed bug with ATC station component, wrong signals for booked stations
* booked stations loading to frequently (for each minor change such as online), changed to timestamp based concept
* update booked stations with receiving ATIS/voiceroom to online
* CDigestSignal class: new class and methods for collecting signals, avoiding too many signals - one of the cures for the performance issues
* fixed bug found during testing, missing start for timers when connecting to network