Added options to switch text font size and position

[bsekachev]

Motivation and context

Default behaviour:

Updated behaviour:

Polylabel algorithm is used to find best place for text (https://blog.mapbox.com/a-new-algorithm-for-finding-a-visual-center-of-a-polygon-7c77e6492fbc)

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)

Resolved #1107

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]

Hi, @nstolyarov

Could you please look at this PR and say us if this is a thing could help you, or maybe suggest other ideas?

[nmanovic]

LGTM, I believe the polylabel is a great solution for the problem.

[bsekachev]

@aschernov @TOsmanov

Guys, could you please update documentation according to these new features?

[bsekachev]

@dvkruchinin Could you please prepare a test? At least font-size should be tested. I am not sure about good approach to test position, but if you have any ideas how it could be implemented, it is great

[TOsmanov]

@aschernov @TOsmanov

Guys, could you please update documentation according to these new features?

@bsekachev Yes, sure

[dvkruchinin]

@dvkruchinin Could you please prepare a test? At least font-size should be tested. I am not sure about good approach to test position, but if you have any ideas how it could be implemented, it is great

@bsekachev Sure. A test will be prepared.