[MRG] Multilabel metrics: `accuracy_score`, `hamming_loss` and `zero_one_loss`

This pull request intent bring 3 new features:

- a tested `unique_labels` and generalized function
- multi-labels support for `accuracy_score` and `zero_one_loss`
- a new metrics the hamming loss (`hamming_loss` ) with multi-label support

Before merging, I would like to suggest to add a new module where multi-labels utilities such as `unique_labels` and ` _is_label_indicator_matrix` are collected.

Furthermore, I have to re-organise some of the function in a multi-label categories. But I will wait that the review is finished.

This pull request doesn't intend to add multi-labels support for every multi-class metrics, but future one might be. :-) This also tackle issue #558.