Automatically load gpx track to map when importing caches

[fm-sys]

Here is a tiny idea that would be convenient: When importing caches from GPX, if that GPX also contains a track, that track should automatically be 'loaded' into the map as well.

I guess it would be good if that were optional; it could be a checkbox within the GPX import dialogue. But probably in 95% of the cases, when people want to import a track into c:geo, it is because they planned an entire caching tour ahead of time, so the situation where the GPX contains both caches and a track is probably the typical case, so most of the time you probably do want to also load the track when importing caches.

Originally posted by @dcjkfgdjhd in #2469 (comment)