Advanced templates

Hi Areski, 

So, here it is, the official PR. 

We (I ...) still need to some cleaning. Mainly, I would like to merge the NVD3Chart with the Mixin class, and 
than remove all the redundant chart classes. 
Also, like we talked already per email, the template "infra" needs to be renamed to base. 

From "user" point of view, there are no changes. Only developers who are using current develop branch might experience difficulties if they directly import the classes, and not use the ones in nvd3 module. 
(E.g, if you do: ```from nvd3.lineChart import lineChart``` your code might break. As a user you should always use: ```from nvd3 import lineChart```).

Once this branch is merged, I will do the clean up, and together with it, I will document how as a user 
you can easily extend the exsiting collections of graphs to include more templates. 

Cheers, 
Oz