Currently, addresses which create things (like bugs@phabricator.example.com) are specified in global configuration. They should be moved to Application configuration instead (Applications > Help/Options > add a new interface here).

• This will reduce the complexity of configuring addresses, and reduce the total amount of global configuration (T5703).
• This interface should check for email address conflicts with usernames (T3404).
• This interface should support adding multiple email addresses (T5039).
• Herald rules should be able to act on which mailing address things were sent to, e..g. to add projects or assign tasks (T5039).
• We should add Differential support (T1476).