GPS::GpsmanData: support for writing DDD files

The module used to write DMS only, but now it can also use DDD also.
The initially read format is preserved, and if not given, it defaults
to DDD.
gps-gpsmandata.t: resolved TODO test (for roundtrip)

Also a minor change was necessary because of changed default (DDD
instead of DMS).
GPS::GpsmanData: track segment support

!TS segments in gpsman files are now marked with the new
IsTrackSegment member.

When converting from or to gpx files, then !TS will be converted
from/to <trkseg>.
test cases for track segment support
gpsman <-> gpx: conversion of track color

Supporting now Garmin's gpxx extension for setting DisplayColor of a
track.
test cases for track color handling
data update