Improve Messaging Options for Header

[Jeremy Hopkins]

Currently messaging displays "notifications" as well as messages between users which can cause problems.

For now we will disable notifications to only show messages between users.

Following this we should add a settings page for messages allowing administrators control over the kind of messages that appear.

[Jeremy Hopkins]

Partial Fix #320 removes notifications from messages. This needs to be put back via admin options at a later time.

→ <<cset 9852cb772a31>>

[Info 3bits]

Issue #319 was marked as a duplicate of this issue.

[Alexander Goryntsev]

Is it possible to improve styling of the messaging dropdown list in the header and make messages' headers use the full width of the dropdown list?