Make the Syncgroup factory methods like the ones for Collection

There is currently a Database.Syncgroup(wire.Id) factory method,
change it to be consistent with Collection.SyncgroupForId/Syncgroup,
where Syncgroup() takes a name and context and the user blessing
is pulled from the context.

MultiPart: 1/3
Change-Id: Ic3e641888193bcf0682959d5f05353e1957de470
6 files changed