R1:6302414883ba

Make the default view of dashboards be just the dashboard

Summary: Fixes T4985, add manage page, change view page to show only panels. Arguably, PhabricatorDashboardArrangeController is no longer necessary. Also, still trying to figure out if I updated all flows that involve "arrange/{id}". Probably missed some. Also not sure of the Manage Dashboard icon. Please advise.

Test Plan: Create dashboard, add panels, "view/{id}" should show just panels, Manage Dashboard should show timeline and edit links.