Add an in-memory database for querying airspace files

[corstian]

As we're already using NetTopologySuite we might as well use their STRtree implementation to facilitate querying the data. Usually this approach is incredibly fast (no overhead from latency, obviously).

Goals:

• Query airspace files locally (and maybe even other types)
• Add helper methods to check what airspaces a Coordinate or Point type is in.