Removing DIPY and CBRAIN

[karanphil]

We need a PR removing the pages about DIPY and CBRAIN. We should refer to CBRAIN in the Freesurfer page.

[zinelya]

CBRAIN was removed in #93. I will add the reference in the Freesurfer page.
For DIPY, I think we should keep it in the documentation as we use it in our scripts. Maybe move it somewhere else more related to coding (like coding standards) ?