After Aphlict reconnects, ask the server to replay recent messages

Summary:
Fixes T12563. If we've ever seen an "open", mark all future connections as reconnects. When we reconnect, replay recent history.

(Until duplicate messages (T12564) are handled better this may cause some notification duplication.)

Also emit a reconnect event (for T12566) but don't use it yet.

Test Plan: {F4912044}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12563

Differential Revision: https://secure.phabricator.com/D17708