Persist excluded recipients when saving mail

Summary:
Fixes T5185. The fundamental issue is that this `excludePHIDs` property was not saved, so the logic went like this:

  - Generate `excludePHIDs` correctly.
  - Pass `excludePHIDs` through the stack.
  - Perform some other computations correctly.
  - Queue the mail for the daemons, throwing it away. {icon bomb}
  - Daemons process mail with empty `excludePHIDs` list.

Store it in the persistent properties array instead.

Also remove the "override self mail" thing, since it's only used by `bin/mail send-test` and suffers from the same issue. I think it's too useless to fix, since even if you get caught by it, `bin/mail` makes it clear why the message was dropped.

Test Plan:
Notable:

  - `exclude` present in properties
  - Exclusion reason under RECIPIENTS header

{P1229}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5185

Differential Revision: https://secure.phabricator.com/D10234