Unified HTML with image banners for non-js users

See https://www.mediawiki.org/wiki/Requests_for_comment/Unfragmented_ZERO_design

* !!! Config is now tests for X-Forwarded-By & protocol for all requests
* When X-CS === "ON", generates banner and config object on the fly
* changed default for bannerWarning - migrating as true, but in new configs - false.
* Generate banners on the fly using imagemagick
* Handle betalabs cluster suffix with a global $wgZeroBannerClusterDomain
* In unified, no longer redirect non-free zero. requests to special,
  show red banner instead

To test, set HEADER X-CS to a valid entity, but also supply X-CS via URL:
* http://127.0.0.1:8080/wiki/Main_Page?X-CS=ON&debug=true

This way the <script> request to the server will have the old style X-CS.
Observe banner, and check that api call is no longer being made.

Disable javascript to see image banners
(I used "Toggle JavaScript" Chrome ext to test)

Change-Id: I8d99e703dc712ef0dfda59e891dfba8674e19c6b