Read GPS coordinates from EXIF tags

If GPS information can be found in the EXIF tags, latitude and longitude will be
extracted and added to the `media.exif.gps` variable. Some ideas how to get the
GPS tags from the EXIF tags where borrowed from Eran Sandler's gist (licensed
under MIT license):

    https://gist.github.com/erans/983821
Add test case for GPS tags

This also adds a sample image licensed under CC-BY-NC from jerquiaga located at
Flickr: http://www.flickr.com/photos/jerquiaga/2394751088/