Minor improvements of z order feature

[bsekachev]

Motivation and context

Resolved #5142
Resolved #2180
Related #3942

• Fixed issue when changing an object causes changing of the current z layer
• Added sorting by z order
• If the sorting is applied, additional indication added to the sidebar

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have added a 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.

[bsekachev]

@klakhov
Could you please take a look?

[bsekachev]

/check

[github-actions]

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[klakhov]

@bsekachev Improvements seem nice to me. I noticed that shortcuts for brightness/saturation ... mentioned in #5142 are not working for me eigther. We have some description about them in docs

Should we add them or remove notes from docs?

[bsekachev]

@klakhov

We do not have these shortcuts anymore for a long time. Since these image settings moved from CVAT settings (F2).
Yes, I will remove them from docs.

[bsekachev]

#5154