Simplify dashboard panel creation

Summary: Ref T10390. Basically hides policy controls when creating a panel on a dashboard. Shows when you edit them or through normal workflow. I think we should maybe also get rid of view policy? Not sure the benefit since results will be filtered anyways. Maybe Text panels? Not sure the use case.

Test Plan: Add a panel, edit a panel.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: hskiba, Korvin

Maniphest Tasks: T10390

Differential Revision: https://secure.phabricator.com/D17393