Implement FIT writing support

Implement FIT writing support

Generate FIT courses from tracks+waypoints. Waypoints get mapped to course
points (generic by default, left/right turns if waypoint names contain the
string "left"/"right" or their equivalents in German, French, Spanish,
Italian).

If the original track contains neither time stamps nor speed values,
a fixed speed of 10 km/h gets assigned to the whole course.

Resulting FIT files have been tested and are accepted by a Garmin Edge 130
unit, but are assumed to be usable with any GPS unit supporting FIT.

Track segement markers are ignored at the moment.