This fixes email threading in Mail.app, that doesn't like when a thread
doesn't have stable recipients.
For instance, here is a possible sender-recipient combinations before:
From: A
To: Me
New issue
From: B
To: Me
Reply on new issue
From: A
To: Me
Another reply
Mail.app doesn't see B as a participant to the original email thread,
and decides to break the thread: it will group all messages from A
together, and separately all messages from B.
This commit makes the thread look like this:
From: A
To: gitlab/project
Cc: Me
New issue
From: B
To: gitlab/project
Cc: Me
Reply on new issue
From: A
To: gitlab/project
Cc: Me
Another reply
Mail.app sees a common recipient, and group the thread correctly.
The goal of suych refactoring is to get rid of observers.
Its much easier to test and code when object creation and all other
related actions done in one class instead of splited across observers,
callbacks etc.
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
