Show "Not a member" message to users not allowed to view a page and that are not members.

Basically, if the user is not allowed to view AND is not a member, tell them that they need to be a member and offer the (request) join button. Also, for invitation only workspaces, a clear message should be shown that it's an invitation-only workspace.

This means that we can also move the content of the Workspace Information panel to the main content of this 'not a member' page.