Export config

Hi Anton

I added another branch with the export config updates.

Main changes
- export is now done in a separate thread (ExportRunner)
- reader and exporter interfaces now support user configuration
- flight mode analyzation is now reusable for other exporters

My idea regarding configuration is: reader and exporter are allowed to create independent configuration dialogs during the export process. ATM there is only the KML export config dialog. I will add more settings to it soon and I will also add a PX4 reader config dialog (to select GPOS).

Also, I'd like to add dialog settings and configurations to the global preferences.

Cheers
ada