Embedded map & map feature collection support

Please review this commit-by-commit.

This contains several things in one bundle.

Updated to styleguide v2.9.1

• Adds .modal__close
• Fixes annoying vertical jump on page initial render due to menu subitems flashing out for a moment
• Fixes bad stacking order on candidate detail page

Map collection home page

Map collection detail page

Individual features defined as GeoJSON features (Point, Polygon or LineString).

Map embedding using a block

This supports points or GeoJSON features.

We're supporting several different map tile providers:

1. OSM Mapnik - the default, doesn't need any other config.
2. Stamen maps - these maps can be used freely. However, sometimes the map server can be down.
3. Two Stadia maps tile styles - these are really nice and available free of charge (unless used on heavy traffic sites) but require registration & API key creation.

When entering GeoJSON features, validation should ensure only meaningful values are entered.

Numbering of individual features within collection uses caching to save queries - I hope we use something else than locmem on production as the invalidation wouldn't work properly with multiple workers/threads/PODs/whatever.

I am a little bit unsure on how to handle new JS and CSS dependencies related to mapping. It would be best to bundle those up. Currently, I left them being served locally file by file but I'm open to other suggestions.