Experiment Branch Improvement

[leix28]

• Fix all docstrings.
  • Evaluator and FeatureToolsWrapper
  • Give a clear explanation about
• Fix Load and Store for prediction problems
  • Used to store executable code for cutoff time, now the only option is repeating cutoff time. We should add a more structured way to store cutoff time in the JSON file.
• Improve feature tools wrapper.
  • Currently, it only support one table which is the event-driven table used for problem generation, we should add APIs to import other tables in the database to assist prediction.
• Add a new walk through using event-driven data.
• Add unit testing.
• After reviewing the code, merge it to dev.