refactor: all classifier models to pytorch

Created by: IgnatovFedor

Models moved to Pytorch

• boolqa_rubert
• paraphraser_rubert
• rusentiment_bert
• rusentiment_convers_bert
• sentiment_sst_conv_bert
• sentiment_twitter

Removed models

• paraphraser_bert (use paraphraser_rubert instead)

Removed components

• bert_classifier
• bert_preprocessor
• keras_classification_model

Updated components

return_tokens constructor argument and attribute is removed in the following components:

• torch_transformers_multiplechoice_preprocessor
• torch_transformers_preprocessor
• torch_transformers_entity_ranker_preprocessor
• torch_squad_transformers_preprocessor