[MRG] Added metrics support for multiclass-multioutput classification

Fix for #3453 
Ping @arjoly . Added support for `zero_one_loss` and `accuracy_score`

The previous two if could be collapsed.

```
if (y.ndim > 2 or not issparse(y) and y.dtype == object and not isinstance(y.flat[0], string_types)):
    return 'unknown'
```