Embed dashboard panels in comments
Summary: Fixes T4983, Panel prefix 'W' should be recognized as a shortcut to a dashboard panel
Test Plan: Open any comment input, type '{W1}', or other existing panel, preview should embed that panel.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: epriestley, Korvin
Maniphest Tasks: T4983
Differential Revision: https://secure.phabricator.com/D9215