webadmin: snapshots sub-tab - ensure model listeners

VMs -> Snapshots sub-sub:
Ensure model listeners existence after sign out.
Re-adding the listeners in presenter's onUiCommonInit method
as VmSnapshotListModel is being initialized on sign in
(along with the other list models:  VmListModel -> initDetailModels).

Change-Id: I006023de74150754d8c79f95b79eb9ad0158b055
Bug-Url: https://bugzilla.redhat.com/1058618
Signed-off-by: Daniel Erez <derez@redhat.com>