KML export

Hi

Thanks for writing FlightPlot, it came in handy already.
I thought it would be great to be able to export tracks for GoogleEarth, so here it is ;). I added a new menu item to start the export process.

It should be no problem to extend it for additional log formats (readers).
There are still a few TODOs but it seems work quite well already.

On the functional side, I would also like to add support for angles later (heading, tilt, and roll).

What do you think?

Regards
ada