new module GPS::Symbols::Garmin

The functions here (get_symbol_to_img, get_cached_symbol_to_img) were
refactored from BBBikeGPS.pm.

Updated also MANIFEST.
GPS::GpsmanData::Tk: display waypoint symbols

Using new GPS::Symbols::Garmin module.
GPS::GpsmanData::Tk: delete photos in destructor
GPS::GpsmanData::Tk: mark functionality also for associated waypoints

That is, in the command callback "-wpt" is set also for associated
waypoints, which is interpreted by GPS::GpsmanData::TkViewer.
Pod work for GPS::GpsmanData::Tk and ::TkViewer

New Pod for TkViewer.pm, which also includes remaining TODOs (some
were previously mentioned as comments).

Updated/fixed Pod for Tk.pm.
show_mark: start animation with "full" mark

Previously the faintest stipple ("gray12") was shown first.
data update