Major update of the website, with a few examples and with some additional minor RFs

Hello everyone, 
I have some initial progress with the website and before the commit messages become way too many to make it easy to review the code I made this PR.

I would recommend to try to make the website yourselves before we merge it to the project. If you go to dipy/docs and run the command `make html` you will get an index.html in dipy/docs/_build/html which gives the first page of the dipy website. I hope you like it. I forgot to say that you need python-sphinx to compile the docs.

With the opportunity of the website PR I want to have your attention in dipy/doc/examples where I started adding examples. Old examples are kept in dipy/doc/examples_0.5 until a bit more cleaning is done.

Especially, in example nii_2_tracks.py (dipy/doc/examples) I have a simple scenario where streamlines are generated with reconstructions made from the TensorModel and the CsaOdfModel and then fiber tracking is generating with EuDX. You will notice that I use peaks_from_model I will do the same in another example for DSI and GQI and remove the caching of gfas from those models. I think it will be fine this way. So, lets not worry more about this. 

I hope that the example addition will be a group effort and that we will kick ass in the way we describe things. The examples that I added now are minimal, more clarification is essential. Please help. Maybe we should setup a hangout for this.

I imagine the doc/examples being separated in the following sections
a) Reconstruction
b) Tracking
c) Segmentation
d) Input/Output
e) Visualization
f) Registration

That is all for now. Stay cool.