- Accumulative support for KID
- Add `backward` and `optimize` method as abstract methods in base training managers.
- Add logging training finished
- Introducing abstract base configurations `configs.BaseConfigs`
- Introducing abstract base managers, including `BaseTestingManager` (abstract `test_step`), and `BaseTrainingManager` (abstract `train_step`)
- Introducing abstract base losses and metrics (`losses.BaseLoss` and `metrics.BaseMetric`)
- Introducing `metrics.AccumulativeFeatureMetric` for accumulative support metrics
- Minor bugs fixed