Don't apply single project logic for some users

Eventhough the project selector may be hidden when there are not
multiple projects to choose from, it is still needed for editing manage
and configuration pages that apply to either specific project or
ALL_PROJECTS.
Here we add a condition that if the user has access to manage pages, the
project selector is never hidden, and both the specific project and
ALL_PROJECTS are available to be used.

Fixes: 0020054