Port of the Picard tagger to /ws/2

by Michael Wiencek for MetaBrainz Foundation Inc.

My proposed project is to update the Picard tagger to retrieve and submit data using /ws/2 instead of /ws/1, in anticipation of NGS. This will involve structural changes to the code to recognize mediums, and updates to the user interface regarding how we display multi-disc releases and "release events," which no longer exist in that form. After the initial work I'll also implement release-type filtering for albums, and investigate a few other features as time permits.