Move event handler for language dropdown out of HTML and into common.  Move language names and language pack selection into common -- lower maintenance costs for internationalization.

R=spertus@google.com

Review URL: https://codereview.appspot.com/14059043

git-svn-id: http://blockly.googlecode.com/svn/trunk@1384 c400ca83-b69d-9dd7-9705-49c6b8615e23