Dubbel layout enhancements

- .hero style (large images at the head of a post)
- padding fixes for dubbel layout
- page-header-title include
- layout options 'hero' and 'no-title'
- About page tests new features with the singel layout

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- reworked dubbel layout
- .narrow figure styles for dubbel
- wide figure styles for dubbel
- big screen scaling for dubbel
- better .site-footer sizing to match different layouts
- ancillary headings
- singel ancillary adjustments