(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
Could you also print in minutes, as in:
<pre>
total_time = time.time() - tic
print("Time Elapsed: %g seconds, %i minutes."  % (total_time, total_time / 60))
</pre>