feat: customizer kirki removal

[sebastianthulin]

This PR has a goal to completly remove kirki framework from Municipio. In this process the following bugs has been resolved:

Customizer

• Live preview of custom css panel (css element in preview is updated automatically).
• When customizing error pages, they are appearing in preview window.

Other

• Backend css editor in admin interface is removed and migrated to customizer css editor.

TODO

These settings needs to be reviewed & tested. If any action plan exists, it can be noted here.

• Footer: Refactor component, to move settings into design builder tool.
• Slider
• Header: Migrate Business, Casual to flexible header.
• Header: Login / Logout styling: Remove custom, move to design center.
• Header: Apperance: Move to design center
• Header: Logotype: Move to site identity
• Helper ColorSwatch: There are a helper for color swatches. This needs to fetch its settings from design center instead of older fields in customizer
• Component appearance: Needs to be reviewed and tested. If settings can be implemented in design center, they should.

[sonarqubecloud]

Quality Gate failed

Failed conditions
1 Security Hotspot
5.5% Duplication on New Code (required ≤ 3%)
C Reliability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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