Improved integration between target_extractor and server

ADA/server/agent/agent.py

ADA/server/agent/communicator.py

ADA/server/agent/dataloader.py

ADA/server/agent/prep_data.py

ADA/server/agent/prep_metadata.py

ADA/server/agent/product_finder.py

ADA/server/agent/review.py

ADA/server/agent/review_annotation.py

ADA/server/agent/target_extraction/product.py

ADA/server/agent/target_extraction/target_extractor.py

ADA/server/agent/train_classifier.py

ADA/server/ios_server/views.py