Extract UserComment Exif data and show it at title

If Exif UserComment can be found, then use it as the image title. There
may be problems with the UserComment encoding as EXIF specifications
are pretty vague on that topic.
Map view for albums in galleria theme

This feature hacks galleria to show an openlayers map instead of the
picture. The pictures are represented by dots on the maps and clicking
them or the galleria thumbnails update the other (and the selected
picture).

By default, the map isn't shown: it needs to be enabled by the show_map
options.