geolocalized-tasks: Add/Remove location to/from a task
geolocalized-tasks: Save last user location to use it offline
geolocalized-tasks: Treat the user location differently than other markers

- doesn't allow the user to delete user location
- use a different color to the tag
geolocalized-tasks: Don't connect the 'button-press-event' twice
geolocalized-tasks: Treat button-release-event instead of button-press-event

LibChamplain does not handle the button-release-event when button-press-event
is being treated by geolocalized-tasks, keeping the cursor as a closed hand.
If we treat the button-release-event, the behavior is according to what we expect.
geolocalized-tasks: Show the location description as its name