Store messages with status

So we know if we sent the stanza, etc
Ping infrastructure

Ping at least every 5 minutes (actually wake up every 4:30, but the interactions can
result in up to 5 minutes).  Prefer to ping when the radio is on anyway
(because we just received or sent a stanza).  Ping at most every 30
seconds during a network event, and at least every 5 minutes when there
are no network events.

Connection manager remembers last ping time and last ping result for
each account.