Help end-users confused by missing nav items

Problem

When an administrator disables a Nav item, end users who are not familiar with the settings chosen may wonder why something they have seen in one project is missing in another.

We have enough UX evidence to know that appearing / disappearing options is a source of confusion when users navigate between groups and projects. With the added flexibility of removing unused features we both simplify the UI by removing dead-ends that admins don't intend users to leverage, but also introduce a species of the same confusion as happens with the group/project distinction.

Proposal

• Add a "missing something?" message with info icon at the bottom of the navbar just above the collapse sidebar divider.
• This message should only be displayed if one or more items have been disabled.
• The mouse-over reads "The following options have been removed by this project's/group's administrator. . See @group-owner-profile for details."