Added support for exporting logfile to KML. 

Currently the KML export settings are hardcoded, but these can be extended to be user selectable.

What can be seen in this screenshot is a UAV track for which the line color indicates the airspeed. There are also timespan points generated every 2 seconds which can be clicked on for further information. The below screenshot does not show all the info, I will provide an updated one tomorrow.

![0bzsmui](https://f.cloud.github.com/assets/1118185/650863/16cd1eb2-d465-11e2-9715-90e2198ecb52.png)

NOTE: This will not work without libkml, which will be the object of another PR.