Touch up basic usability of Dashboards

Summary: Ref T10390. This mostly shuffles layout into "View" and keepts "Manage" around for Edit/Copy/History. This feels better to me overall. Also tweaked some spacing and color.

Test Plan:
New Dashboard, edit Dashboard, shuffle panels. Create new panels.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T10390

Differential Revision: https://secure.phabricator.com/D17326