JavaScript optimizations

I refactored the base template a little bit:
* I removed the YUI dependcy because it was only used for a small code function which could be replaced with jQuery code. This will speed up initial loading times a little bit and reduce external dependencies
* The JavaScript code used can be optimized a little bit more by removing .ready() and caching the ".go-top" class
* Last but not least I updated jQuery to 1.10.2 (still supports old IE versions, which might be dropped by using jQuery 2.x.x)
* There was a unnecessary closing div tag after the content, which I removed

All these changes don't influence the appearance of the theme.