(WIP) Sparse models: S-LASSO and TV-l1

- Supports TV-l1 and S-LASSO priors
- Supports logistic and squared losses
- Has cross validation
- Can automatically select alpha by CV (+ automatic computation of useful alpha ranges for the CV)
- Warning: User must supply l1_ratio
> > +    from sklearn.linear_models.base import center_data
> > +except ImportError:
> > +    from .sklearn_basic_backports import center_data

> You mean in a separate module toto.py so that one could then do:

Sorry, this is a brain fart. Please ignore this comment.