Allow blog resources to be served without Celerity

Summary:
Allow skins to serve arbitrary resources without needing to be mapped, so we can have a vibrant community of amateur skinners.

For "basic" skins, just put all the "css/" on the page always.

Includes an image to prove that works.

@vrana, pretty sure this has no impact outside of Phame but it does change Celerity so it might be to blame if there's any weirdness with static resources.

Test Plan:
{F21341}
{F21340}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1373

Differential Revision: https://secure.phabricator.com/D3719