Noam/mon 1644 enable f1 as a default metric

[noamzbr]

What does this implement/fix? Explain your changes.

1. Add f1 to binary tasks
2. Even in binary, I may want to use multiclass metrics to get all kinds of metrics that consider both classes (e.g., I may want to use f1_macro to consider also a very un-common 0 class).