Option to disable the status message "In development mode."

Problem/Motivation

If the option "Activate developer mode" is enabled, a permanent status message "In development mode." with a "Go online" link is displayed. When enabling the developer mode on a production site this absolutely makes sense, but when working with a dev/test/prod setup constantly seeing this message is just annoying.

Side note: The link text "Go online" can be confused with the "Go online" link of the maintenance mode if one doesn't read the text before the link. Better change the link text to "Turn of developer mode" or similar.

Proposed resolution

Add a configuration option (so it can be differentiated for different environments in a dev/test/prod setup using config_split → ) whether to show the developer mode status message or not.