Every task write went straight to the API, so offline a new task failed with
"Network Error" and was lost, and a tick flipped back. Tasks now go through
todoRepo and the mutation queue like packing items: a temporary row at the
end of the list offline, the edits and the delete of it wait for its real id,
and an online write to a task that still has an older one queued joins the
queue behind it, since task writes carry no version token. A reorder offline
is queued without the tasks that have no server id yet. Desktop and phone
both write through the store, so both are covered.
Refs #2601
Maurice