Remove Zepto and include jQuery 2.0.0

jQuery has become the de facto standard JavaScript library on the web. Switching to jQuery 2.0.0 means we remove support for Internet Explorer 6, 7 and 8.

Reference #152.

We should be aware that jQuery 2.0.0 is still bigger as Zepto:
Zepto: 26.6 KB, 10.1 KB gzipped
jQuery: 81.1 KB, 28.9 KB gzipped

These numbers might be irrelevant when concatenating and minifying all scripts.