With the new UI, the broadcast message is the first level child element
of the body tag and then render full width without respecting the width
of the left sidebar. This makes the message goes under the left sidebar
in smaller screen.

This commit fixes the issue by moving the message element into the
"page-with-sidebar" div so it will always render together with the main
content area with same look as before. The rendering for the search,
login and other view without left sidebar remains untouched.

Releases: master, 7-7-stable
Fixes: #1019

Added tests and updated docs. Also adding 'user_id' field in the hooks for adding/removing user from team.