Add a batch location update option

As requested in issue #2, those commits add an "Update Locations" options in the pop menu of the projects explorer.
It filters the selected projects: only the closed ones can be updated.
The update is done on the common prefix of the location URI:
- if a project in the selection has a different location (like /opt/git and /var/git), the update will be refused
- If you have 2 projects /var/git/project1 and /var/git/sub/project2, you can replace the /var/git/ part by a new one, say /var/gitolite. The results will be /var/gitolite/project1 and /var/gitolite/sub/project2.

Finally, a LocationUpdater utility class has been created to centralize the location update process.
Although, I didn't updated the PropertyPage code to use this new class.

This version lacks logging and some dialogs to notify the user of the operations/errors.
It also lacks internationalization methods.