TODO list:

- show a picture preview on mouse-hover (blocked by lp:1017243)
- if multiple pictures have the same location, show a list with
   picture names on mouse hover
- add a screencast to show the tagging process
- more tests
- add a "go to" menu entry to go to a specific position
- add a menu entry to go to selected image
- add a path-layer to show a path of the listed pictures ordered by
   date/time. then you have a map with the way of your travel route.
- be able to order the picture list by date/time, by name, by long/lat
- be able to delete a geotag from a picture