Restore article scroll after closing Media Viewer

There used to be a CSS trick with the order we added things to the
page and removed them from it, but it doesn't seem possible anymore
with the new order of execution, with the overlay appearing
immediately and being taken care of inside bootstrap.

The main cause of the bug, however, was the hash reset happening
after the interface was closed.

Doing the scroll restore with jQuery.scrollTo is more future-proof
and testable in QUnit.

Additions were also made to the cucumber E2E test because QUnit
alone wouldn't have caught the hash issue.

This also cleans up custom events a little and reintroduces
pushState on browsers that support the history API.

Change-Id: I63187383b632a2e8793f05380c18db2713856865
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/439
Bug: 63892
Merge "Restore article scroll after closing Media Viewer"