Reintroduce versioning & bump to 2.1.0

Beginning versioning from the last recorded number which was 2.0.0.
Version format from http://semver.org/

This version includes initial work completed in the
https://github.com/alphagov/Accessible-Media-Player fork including:

- introduction of Jasmine testing framework & phantomJS test runner
- new architecture for mediaplayers
- namespacing for all global variables
- support for youtube defaulting to the Iframe player
- unit and integration tests for new architecture