[MRG] Multilabel-indicator roc auc and average precision

The goal of this pr is to add multilabel-indicator support with various types of averaging
for `roc_auc_score` and `average_precision_score`.

Still to do:
- [x] Implementation of micro, macro, weighted and sample `roc_auc_score`
- [x] Implementation of micro, macro, weighted and sample `average_precision_score`
- [x] Add a general test for binary metric that are extended through averaging
- [x] Harmonize how global tests are performed for the metrics module
- [x] Write the narrative documentation
- [x] Ensure that the scorer interface work with both possible representations (see #2451)
- [x] pep8

A priori, I won't add ranking-based `average_precision_score`. 
I don't want to add support for the `multilabel-sequence` format.