* typo getRemoteAircraftsData -> getRemoteAircraftData (no "s")
* typo getEelevationAtPosition (double "Ee")
* get functions "const"
* added unit for some variables such as latitudeDeg
Instead of requesting it individually for each callsign and waiting for a
signal from xswiftbus, pass in a list of callsigns and use async callback
to read the data.
QtDBus was the main component of xswiftbus' Qt dependency. This is the
first preparation step to get xswiftbus Qt free.
The new implementation is based on the low level libdbus library, which
was also in use by QtDBus itself. But instead of QtDBus, we use now a thin
C++ wrapper. To keep DBus handling async, libevent is used to monitor
timeouts and fds.
