Drawing style for loaded geodata file

[Tobias Leupold]

Hi Marble devs!

Via MarbleModel::addGeoDataFile, I can load e. g. a GPX file to be displayed
on a MarbleWidget. This seems to work fine, it's loaded, added and waypoints
are also represented as little flags.

The track itself is however hardly visible, as it' drawn as a one-pixel-width
white line. How can I adjust the drawing of a geodata file?

Thanks for all help!

Cheers, Tobias