Hide Manage Forms from non-admin users. Refs T683

Summary: Hide the Manage Forms menu item from non-admin users. This doesn't prevent non-admins from accessing /settings/forms though. If that's necessary as well, I could use some advice on the best way to accomplish it (redirect from the marionette controller?)

Test Plan: Follow test plan from T683 (make sure form_wizard feature is enabled in features.php)

Reviewers: shadowhand, rjmackay

Reviewed By: shadowhand

Maniphest Tasks: T683

Differential Revision: https://phabricator.ushahidi.com/D335

Conflicts:
	web/media/js/app/util/App.handlebars.js