Add modicon source and preview

[victorpopkov]

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• I understand that if I ignore these instructions, my issue may be closed without review.
• I have made sure that there are no similar opened issues.
• I have made sure that the mod version matches the latest release.

Is your feature request related to a problem? Please describe.

The source of modicon.tex (in PNG format) should be added to the repository with the original quality that will be used as a reference. Adding preview image (either PNG or GIF depending on the animations' availability) should also be considered to use as a preview in a README.md.

Describe the solution you'd like

Add modicon.png and preview.gif.

Describe alternatives you've considered

If applicable, add a clear and concise description of any alternative solutions or features you've considered.

Additional context

If applicable, add any other context or screenshots about the feature request here.