Add 4 packages for convex optimization

This PR adds recipes for 

- [cvxpy](http://www.cvxpy.org/en/latest/)
- [cvxopt](http://cvxopt.org/)
- [ecos](https://github.com/embotech/ecos-python)
- [scs](https://github.com/cvxgrp/scs)

cvxpy is quite useful, and the other three are solvers it uses. The latest release version of cvxpy doesn't support python3. As of this morning, the master branch _does_, so when they make their next release, this will need to be update. The other three packages do support python3.