Allow Maniphest to process multiple commands via email
Ref T7199. Two notable changes:
- Process multiple commands.
- Process commands when creating or updating a task.
And generally clean things up a bit.
- Used receive-test to execute all commands for new tasks.
- Used receive-test to execute all commands for existing tasks.
- Used a combination of commands to produce varied effects.
Reviewed By: btrahan
Maniphest Tasks: T7199
Differential Revision: https://secure.phabricator.com/D12234