Add ability to geotag images interpolating times against tracks.

Add ability to geotag images interpolating times against tracks.

Geotag information is saved (when specified) as EXIF GPS information using the built in libjpeg component of libexif. (EXIF writing using libexif is more complicated than one would wish!)

The geotagging can be invoked 3 ways:
. Directly updating an image that is already on a waypoint
. For specified images on a TrackWaypoint layer (all tracks with the layer may be used interpolating a match)
. For specified images on a specified Track

Various options are given to the user to control the geotagging process:
. Whether to write EXIF
. Whether to create Waypoints from the images.
. Whether to Overwrite existing GPS information
. Timestamp issues:
	- Whether to change file modification time
	- Time offset between creator (normally the camera time) and actual GPS UTC time
	- Cater for time zone setting of the creator (again normally the camera setting)

Much of this work has been inspired by GPSCorrelate. (http://freefoote.dview.net/linux_gpscorr.html)