Fix encode_plus
Add options to control more precisely the output of `encode_plus`.

All the outputs that can't be ingested by a model as deactivated by default.
`token_type_ids` can be ingested by most models and if thus activated by default but can be turned off.

Fix #1532 among others
Looks good to me, this philosophy (only model-inputs and optional non-model-inputs) seems way better to me than the previous one.