Adds satellite map layer, closes #31

[daniel-j-h]

This adds a new satellite raster layer, see #31.

Tasks

• Get some eyes on the translation; are the words for pl and uk fine, folks?
• Decide if the raster satellite layer is useful as is already, or should we somehow combine raster and vector data? At the moment the raster layer alone e.g. does not show any labels from the basemap data. Maybe still valuable when zoomed into cities, and so on?
• Create a Mapbox account for this project associated with this project's mail, and get a token into the layer.
• Ask the mapbox folks (see issue add satellite image from mapbox #31) for an API rate limit raise, they're all lovely folks.

[daniel-j-h]

Please check these 🙇

[daniel-j-h]

Add the project-specific token here, once we have a Mapbox account for this project.

[ttomasz]

Hi @daniel-j-h thanks for the PR. Unfortunately you just made it as we finished splitting up the style from the map which kind of makes this PR obsolete but we did try to use as much as we could from that in #55 so at least it saved us some time on reading mapbox docs and figuring out the right url and attribution :) I'll close this one and let's keep going in #55 .