Add header through build & give build config

Build script will now build only for the players specified
Merge branch 'master' of github.com:alphagov/Accessible-Media-Player into youtube-iframe-player-corrections

Conflicts:
	compress_js.sh
Correct bashisms

As reported by http://man.he.net/man1/checkbashisms
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
Merge pull request #2 from alphagov/youtube-iframe-player-corrections

Youtube iframe player corrections