Begin modularizing profile panel/link construction

Summary: Ref T10054. This has no product impact, but prepares us for customizable side nav on "profiles" (today, projects; probably users some day; and maybe other stuff down the road).

Test Plan: Clicked all links on a profile, everything was exactly the same as before.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10054

Differential Revision: https://secure.phabricator.com/D15007