(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
Fixed th max_iter stuff.
For the moment there's no py3 anticipation. There are other non py3" stuff like `print "Hallo!"` lurking in the code base.