Use the new Datumaro dataset class (#1785) instead of the old one in the implementation of the OTX dataset classes and data loaders. Also replace the OTXDataItem class with the new Sample class.

The following dataset types and features must be supported:

• Classification
• Detection
• Instance segmentation
• Keypoint detection
• Segmentation
• Tiling
• Multi-label and hierachical classification
• Ellipse