Fix diff cli, add confusion matrices for polygons and masks

[zhiltsov-max]

Summary

• Fixed the diff invocation problem with missing class methods
• Added test
• Added confusion matrices for polygons and masks
• Added support for mismatching classes
• Fixed ProjectDataset.Subset

How to test

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2020 Intel Corporation
#
# SPDX-License-Identifier: MIT