Airport selection on Map

[FlyingFoxVATSIM]

At the moment users can only select airport information when they are staffed with ATC. The middle mouse button has to be used to click on such airports.

It may be more intuitive and efficient to right click on a map position and then not only list FIRs and UIRs, but also airports within a certain radius.

My suggestion: search within the area of the circle, but capped at a radius of 20 NM.

[marvk]

#53 will be closed when v0.3.0 will become the stable version, so any issues that arise from the improved selection implementation should be discussed in #74 or in a new, separate issue.