feat: grid column settings in theme

[aaron1604]

Proposed changes

Added Grid columns settings in Theme settings. Now instead of the default 24 grid columns, you can customize it through theme settings.

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• [ x ] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
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Further comments

Grid column settings are there in theme settings.

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[FalkWolsky]

A wonderful contribution. Thank you very much!