Detection for nested folders (CLI)

[sizov-kirill]

Summary

1. This PR repeated functionality that was implemented in Detection for nested folders #623, but now recursive search is working in CLI command as well.

2. Changed strategy for recursive format detection: the function env.detect_dataset now returns a list of detected formats at all recursion levels (in case when each step of recursion returned a more than one format).

3. Fixed detection for LFW format.

4. Added detection for Cityscapes format.

5. Open Images: allowed to store annotations file in root path as well

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) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT

[zhiltsov-max]

Please fix conflicts.

[zhiltsov-max]

Please update changelog