append lat,lon,dist to clipboard and print distances on load-from-track

[Jochen]

These changes append coordinates with distance to clipboard on measurement instead of replacing clipboard. Add distance measurement to load-from-track and print it to console.

I use foxtrotgps to measure the tracks I have driven - without gps data. Although foxtrotgps has this function, but there is no possibility to save it. I would also like to be able to load these tracks with a distance measurement. For this I have implemented the following ideas in the code:

- with the distance measurement the coordinates are attached to the content of the clipboard instead of being exchanged
- these coordinates are not appended to the clipboard with "lat - lon", but with "lat,lon,distance distunit".
- when loading tracks, the distance per coordinate is calculated and (additively) output in the console with g_printf().

These small adjustments make it possible for me to measure tracks with foxtrotgps by hand and save it as track via clipboard in a text file. Furthermore I can read these files afterwards with foxtrotgps (and other lists with coordinates) and have the track measured (distance).