Set messageIDHash from SendGrid and Test controllers

Summary:
Most mail comes in through the script, but we can also generate it with the test controller or the SendGrid receiver.

In these cases, we produce a `null` message hash ID, which fails on inserts into MySQL databases configured in strict mode.

Instead, correctly generate the hash ID in these cases (for tests, make one up).

Test Plan: Generated test mail. (I'll see if @sokcevic can test SendGrid).

Reviewers: btrahan

Reviewed By: btrahan

CC: sokcevic, aran

Maniphest Tasks: T2423

Differential Revision: https://secure.phabricator.com/D4667