Zeitgeist should save a user friendly file name

The file name shown by gnome-activity-journal uses the "text" field from the zeitgeist database, but since the zeitgeist logger is not writing to that field, g-a-j finds it empty and picks up another field to show, in many cases it ends up being the ubuntuone:uuid field, and our log on g-a-j ends up looking awful.

To fix this we should write the file name part of the file path in the zeitgeist db, to be picked up by g-a-j.