Documentation update

[TOsmanov]

Resolve #3450
Resolve #3417

Motivation and context

This PR contains:

• updated "AI tools", "Open CV tools", "Settings" , "Top panel" sections, updated image155.jpg and add image221.jpg, image222.jpg, image223.jpg
• updated "Vocabulary" section and add approximation_accuracy.gif
• updated other section related to adding a "Done" button

How has this been tested?

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

[bsekachev]

I see you also considered not merged PR, so, its interface was updated a bit.

[bsekachev]

@TOsmanov

Thank you for preparing docs.