AnomalyCache class

[VargBurz]

This PR adds new AnomalyCache class which is used in AnomalyDetector instead of dict.

Changes:

• add new AnomalyCache class with:
  • required fields: alpha, confidence, enable_bounds
  • optional fields: seasonality, segments, time_step
  • method set_segments, which sets self.segments wrapped in SerializableList
  • method get_enabled_bound, which returns self.enable_bound wrapped in Bound
• uses meta.JSONClass decorator for AnomalyCache
• utils.meta:
  • add SerializableList class, which extends list with to_json method
  • add method serialize which returns object.to_json() if object has to_json method
  • JSONClass.to_json uses serialize method for class fields
• replace dicts with AnomalyCache in AnomalyDetector's methods: train, detect, process_data, get_window_size
• rename enable_bounds to enabled_bounds in AnomalyDetector
• move enum Bound from AnomalyDetector to detector_typing
• fix unit tests
• add test for utils.meta.serialize method