R1:af84f215f9b8

Move lingering "Aphront" classes to Phabricator

Summary: Ref T13395. Moves some Aphront classes from libphutil to Phabricator.

Test Plan: Grepped for symbols in libphutil and Arcanist.

Maniphest Tasks: T13395

Differential Revision: https://secure.phabricator.com/D20975