Added $.each function.

Added $.each to allow iterating over arrays, array like object and
objects with an interface similar to [].each().
Updaded unit tests for core.js to include $.each.
Fixed indentation on unit tests.
Fixed bug in $.UIGoBackToArticle.

When using $.UIBoBackToArticle articles and navs with “previous” class
were not getting set to “next”, making them unable to navigate to
properly. This has been resolved.