Implement mediawiki-storage lib

This library is intended to permit Dashiki and other projects
to get json content from mediawiki pages. To avoid cross origin
problems, mediawiki-storage uses jsonp. It is put together as
a bower package, it uses karma for testing and gulp for building.

Bug: 68448
Change-Id: I8f94f9f5df7f2146e25b1d08a21d77b91a59f9d1