(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
Ensure C ordering

or ravel only once

or

```input_img_flat = input_img.view()
input_img_flat.shape = input_img.size,
input_img_norm = np.dot(input_img_flat, input_img_flat)```