Summary:
Ref T4222. This fixes some issues with Phame's resource construction.
Phame requires a fully virtual resource source, and since I want to run wordpress templates unmodified some day I don't want to build resource maps for skins.
Move all the stuff that depends on resource lists being discoverable at build time to `CelerityPhysicalResources`, and only generate maps for subclasses.
The root `CelerityResources` can now construct virtual resources; construct a virtual resource for Phame and use it.
Test Plan: Off-domain blogs work correctly now. On-domain blogs with custom skins work correctly now.
Reviewers: btrahan, hach-que
Reviewed By: hach-que
CC: aran
Maniphest Tasks: T4222
Differential Revision: https://secure.phabricator.com/D7873
