Refactored Parameter Validation and Unified TiledDataset Class

[TibbersHao]

This PR covers changes as a reflection to the 2nd Diamond Hackathon's discussion.

Feature Upgrades

• [x] Refactored the Parameter Class for Pydantic BaseModel to lift the nested structure from last version, thanks to @dylanmcreynolds !
• [x] I/O: Now both train.py and segment.py will only take one argument yaml_file_path.
• [x] Tiled Dataset: The InferenceDataset has been taken out and TrainingDataset has been modified to a unified TiledDataset which will handle both training and inference.
• [x] Testing: Example yaml files have been provided as a template under a new directory.

To Test:

1. Modify the tiled_api_key for all clients under each example yaml file.
2. Modify the uid if necessary.
3. In terminal, make train_tunet
4. In terminal, make segment_tunet