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