Add variant option color on product page in demo store

[SergeyAsadchiy]

WHY are these changes introduced?

This adds the usual functionality common to e-commerce

WHAT is this pull request doing?

This implementation allows the user to see the colour of the product variants and select the product of the desired colour

• Clicking on a coloured square will take you to the page of the selected product variant.
• The selected colour variant is highlighted with a frame
• Unavailable colour variant is crossed out with a diagonal line.

HOW to test your changes?

• Go to a page of product that has several colour variants
• Here you will see squares with the colours of the product variants.
• Click on a colour you want to go to the page of the selected product variant.
• Chek selected and unavailabled pvoduct variants
• Check with browser dark theme

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[SergeyAsadchiy]

I've signed the CLA!

[SergeyAsadchiy]

I've signed the CLA!

[SergeyAsadchiy]

I've signed the CLA!