Feature/standard generator

A new IRenderingElement generator based on IUPAC recommendations and Clark A 2013. This patch adds the rendering I started ~7 months ago, it took about 4 rewrites to clean up but I'm more or less happy with it now. 

The atom rendering is split across multiple classes and reasonably well tested and has parts that can be reused. Unfortunately the bond generation is still complicated and difficult to test. This seems to be the case with the other generators though.

Still a more to do, namely:
 - more documentation, need to reference the Clark paper and will write a wiki page / blog post
 - better parameters that incorporate wikipedia/journal structure settings
 - highlighting / backlighting
But these features are supplementary and can be added after.

- Clark A. 2013. http://onlinelibrary.wiley.com/doi/10.1002/minf.201200171/abstract