Broadcast messages don't show up on various pages

Created by: thasmo

On some pages the global broadcast message isn't displayed:

• User profile (/u/[user])
• Profile settings (/profile/*)
• Group settings (/groups/*)
• Project settings (/[group]/[project]/edit)
• Admin area (/admin/*)
• Public homepage (/public)
• Probably more

In addition it may make sense to have an option "is public" for messages. And, if there's an API for reading messages, also GitLab CI could display them.

Thanks for the awesome work btw! :)