Remove Copy Dashboard

Summary: Ref T10390. This removes the "Copy Dashboard" feature, which was more of a crutch to assist in the complexity of building and maintaining dashboards. I think we're close enough now that removing this and adding in some simpler edit dialogs should negate any benefit to keeping this around. Also removed an un-used "Uninstall Dashboard" dialog.

Test Plan: Visit manage, edit, no longer see option to copy dashboard. grep /dashboards/ for "copy" and remove all traces. Add some panels to a dashboard I own.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T10390

Differential Revision: https://secure.phabricator.com/D17338