Use EditEngine for Conpherence preferences

Summary: Ref T4103. Only trick here is hiding the panel if Conpherence is not installed.

Test Plan:

• Edited Conpherence preferences.
• Uninstalled Conpherence, saw panel vanish.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4103

Differential Revision: https://secure.phabricator.com/D16022