Support for VGGFace2 dataset format

[yasakova-anastasia]

Motivation and context

Add support for VGGFace2 format support

How has this been tested?

Unit tests

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

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

[coveralls]

Coverage increased (+0.006%) to 72.124% when pulling 07b1b2b on ay/add-vggface2 into 9b62b71 on develop.

[zhiltsov-max]

Probably we need to fail, if an image has mismatching labels in annotations or if there are wrong point sets (!= 5).