Implement the "!priority" and "!status" mail commands
Summary: Ref T7199. Adds "!priority" and "!status".
Test Plan:
- Used !priority and !status to adjust tasks.
- Changed config and provided keywords.
{F355976}
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T7199
Differential Revision: https://secure.phabricator.com/D12248