places-menu: Mark mounts that can be unmounted as removable
While the eject() code falls back to unmount() for mounts that
don't support ejecting, it's not possible to actually do so
because we hide the eject button.
Fix this by treating all mounts as removable that can either be
ejected or unmounted.
for !152 with master
1 minute and 14 seconds
(queued for 2 seconds)