Let dashboard panels render in a very basic way

Summary: Ref T3583. This implements very primitive panel rendering on the panel detail page, and an ajaxable standalone view.

Test Plan:
{F149135}

{F149136}

{F149137}

{F149138}

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T3583

Differential Revision: https://secure.phabricator.com/D8913