Prepare Profile Panels for adoption in other applications

Summary: Ref T10054. Take specialization off the objects and put it on Engine subclasses instead. One reason for this is that certain objects (like users) might have multiple different sets of panels in the future (e.g., their user profile and their home page).

Test Plan:

• No user-visible changes.
• PanelEngine no longer has any hardcoded "project" stuff.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10054

Differential Revision: https://secure.phabricator.com/D15018