Plugging things back in: Translator features/ sharding

[TimotheeMickus]

Setting a shard_size different from 0 currently causes the model to duplicate the test set.

The simplest way to circumvent this at the moment is to set the flag -shard_size 0.

Currently, the src_feats_shard has been commented out: i.e., manual features can't be provided to the model for now.