* avoid unnecessary loads via DBus * fixes wrong m_validCallsign values (not updated) * no signal when edited but no value changed
* CSharedStringListCompleter utility class supporting timestamp checks * avoid unnecessary DBus transfer * less memory consumption Remark: No totally clear if a QCompleter can be shared, but I have not noticed a problem so far
* completer used in 3 places, makes sense to encapsulate as class * automatically updating from network context