Fixes #17411, #17412 for empty changelog/roadmap

This change provides the user with a message that explains why the change log or roadmap pages are empty.

- Changelog message wasn't explaining what is going on.
- Changelog message wasn't showing when there were no issues, only when there were no projects.
- Changelog message formatting was using page title style.
- Roadmap had no messages.
- Roadmap had a variable to check usage that wasn't being used.

Now we show a different message based on whether the user is manager (hence can create versions)
or a regular user.

Conflicts:
	changelog_page.php