Improve aircraft selection / listing in UI

[TwinFan]

Current Situation / Problem (follow up to #9)
Aircraft selection for a/c info window or in settings is currently by typing only: transponder, registration, call sign, flight number...
As there is no list of aircrafts to choose from the user has to know somehow that the aircraft is there. Currently only possible by reading the labels of the displayed aircraft, which only works for aircrafts closeby.

Suggested Alternatives

• List window, which just lists all aircrafts with some values. Real benefit with
  • customisable columns with live data
  • filter options to limit displayed a/c (like distance to viewer, a/c type...)
  • action from there like "Open Info Wnd" or "Copy trsp to Clipboard"
  • will finally require to adapt a ListBox into TFWidgets.cpp, see TestWidgets.cpp by Sandy Barbour
• Click on a/c
  • Challenge: Don't know if it is possible to map aircrafts 3D-coordinates to the 2D coordinates a mouse click has. Meaning: Unclear how I would identify the closest aircraft.
  • (Above TestWidgets.cpp has a solution to temporarily receive mouse clicks in the entire screen...they use it to close a drop down box)

Benefits
Enables the use to see and select from all aircrafts currently being handled by LT.

[TwinFan]

For clicking make use of the 2D coordinates that now have to be calculated for label drawing (#63).

[TwinFan]

Shipped with v2.09.