New `volt` theme

[Mathias M.]

• New volt theme based on the volt boostrap theme
• Use very few components from this theme and make sure everything is included in the single HTML output
• Add a screenshot in the README

[Mathias M.]

See https://github.com/themesberg/volt-bootstrap-5-dashboard

[Mathias M.]

Too many security issues + broken build. Let's not use this theme.