Improve the empty state for frequently visited links in the Projects/Groups menus

Proposal

One of the issues of the "Frequently visited" links is due to the fact that the list is empty for some users because of the reliance on local storage.

For handling this empty list we can add an empty state in place of the blank area.

• Promotes search functionality for first time users of GitLab
• For users who have issues with local storage the empty state provides something useful

Current	Projects w/ empty state	Groups w/ empty state