Separate "PhabricatorBarePageView" out of "PhabricatorStandardPageView"

Summary:
For Phame, we really want more than a chromeless page -- it shouldn't have Javelin or Phabricator styles on it.

Pull the bare infrastructure out of StandardPageView and make it available as BarePageView.

Test Plan: Viewed bare page in UIExamples, various non-bare pages.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3711