Avoid the application becoming unresponsive during nav-cache rebuilds. We still have to wait for the rebuild, but perform it on a helper thread so the main GUI thread stays responsive and hence doesn't trigger a beach-ball / 'not responding' alert. Also ensures there's some feedback (the spinner) during the rebuild operation, so users don't think we've hung.
Cache the parsed navigation and airport data in a binary file to reduce
startup times and memory consumption (since only referenced FGPositioned
elements are held in memory).
Data will be reimported when the mod-time of any input file is changed.
If a global file is changed (nav.dat, awy.dat, apt.dat, etc), the cache
will be completely rebuilt, which takes approximately 30 seconds on
moderate hardware. (Future work may reduce this).
