Admin edition filter redesign

Updates the UI for the admin index based on Stephen's designs.

As well as getting the tests green after @bfirsh and @russellthorn's work, I've taken the liberty to add some spit and polish:

* Tweaked the layout to give more space to the filter and adjust, whilst tweaking the table column widths so that only the title column is fluid.
* Updated the JQuery chosen library to the latest version, which works better with responsive layouts.
* Improved the document type filter option so that sub-types are organised into optgroups and made `Admin::EditionFilter` work with sub-type ids, rather than plural names.

I still think the date range filtering could do with a bit of work to make it friendlier, but it's time to move onto another story now.

Tracker: https://www.pivotaltracker.com/story/show/55456670