Raphael update, updated network graph tooltip

Updated RaphaelJS from 1.5.1 to 2.1.0, probably need to change repository to gitlabhq/raphael-rails in the Gemfile 


Made branch-graph.js more readable by abstracting methods.
Updated tooltip of network graph to be better readable and nicer looking.  Screenshot below:

![Screen Shot 2012-12-28 at 16 33 32](https://f.cloud.github.com/assets/351038/40939/db836720-55c1-11e2-86ba-438529a5ea09.png)