Refactor code for performance and maintainability

I started a major rewrite of R2D3. The goal was to increase performance as well as maintainability. I'd like the code to be clean enough anyone can jump in and contribute.

* Wrap Raphael/Dom node in a single wrapper rather than extending Raphael
* Delay Raphael node initialization until all required attributes set
* Allow DOM Node to directly reference R2D3 wrapper
* Enable event binding for groups
* Enable setting SVG height/width via css
* Use switch statements over if blocks for performance