upgrade knockout to 2.3.0 and swith to minified version

As far as I can tell there aren't any breaking changes.

Relevant release notes:

http://www.knockmeout.net/2012/10/knockout-2-dot-2-is-out.html
http://www.knockmeout.net/2013/07/knockout-2-3-0-is-out.html

@biyeun