Fix sizing of jumbo at certain cutoff + bad interaction with grey background on some sizes
Fix sizing of jumbo at certain cutoff + bad interaction with grey background on some sizes

- The jumbo background was layed over grey-background elements further down, resulting in the background looking like it didnt cover all of its content. z-index: -1 on the jumbo fixes this.
- The minimum height of the jumbo was not adjusted for the new implementation of the slant (needs additional 300 px). Fixed this.

CopenhagenCityArchives/kbh-billeder,CopenhagenCityArchives/kbh-billeder,CopenhagenCityArchives/kbh-billeder