Combine the "View", "Arrange", and "Manage" modes of Dashboards into a single mode

Summary:
Depends on D20361. Ref T13272. Currently, Dashboards have three separate modes: view, arrange, manage.

With the advent of Portals, I think we can simplify this, and make the dashboard view a combined view/edit/manage page. To view it in a cleaner standalone way, you can add it to a portal/home/project. I'll also improve the "Install" workflow.

Test Plan:
Viewed a dashboard page, clicked through all the actions, grepped for affected URIs.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13272

Differential Revision: https://secure.phabricator.com/D20362