Remove `New project` button in group overview if visibility levels are restricted

What is the problem we are trying to solve?

If you have Private checked under the Restricted visibility levels field in the admin area then non-admins can not create projects in private groups.

Proposal to solve this problem

When Private is checked under the Restricted visibility levels setting the New project button on a private group should not be shown.

Designs

Remove button outlined in red

Engineering implementation plan

This issue and #384514 (closed) may be able to be solved at the same time.

• Update permissions check in app/views/groups/_home_panel.html.haml#L2