Implement Product Review Sentiment Pre-Built Model [resolves #221]

[irmakyucel]

• Implement hyperparameter optimization.
• Use optimized parameters in final model build and cv methods.
• Use fit instead of partial_fit because PassiveAgressiveClassifier did not work well with partial fit.
• Update README for 3-fold and 5-fold cross validation scores.
• Add a test case for load and prediction of product review sentiment prebuilt model.

[husnusensoy]

can you reimplement the model using icu tokenizer.

[husnusensoy]

Score is too low. Please try to find root cause and use a classifier with predict_proba function

[husnusensoy]

@irmakyucel please do ensure that

1. you send your pull request to develop branch
2. You sync your ( by merge ) feature branch with development branch first and resolve conflicts.
3. @dafajon kindly requesting your support.

[dafajon]

This PR is re-implemented with #238 closing it.