webadmin: add memory column to snapshot subtab

Add column to the snapshot subtab that contains checkbox which reflects
whether the snapshot contains memory state or not.

Change-Id: Ic9a5159f84fff98377526da336759445e41068f3
Bug-Url: https://bugzilla.redhat.com/960931
Signed-off-by: Arik Hadas <ahadas@redhat.com>