UI/feature updates

Internationalize the entire app:
- A new "user preferences" dialog allows configuring the language. By default, the language is auto-detected from the browser language.
- Units can also be switched to the US Customary system in the user preferences.
- The German translation is finished an Norwegian and Russian translations have been started. Translations are created collectively on Weblate.
Add shower POI type, simplify POI categories and add “All amenities”, “All touristic places”, “All sports facilities” and “All shops” POI types (#261).

Technical changes

The FacilMap modules are now internationalized using i18next. Find details about how to adjust the language configuration in the documentation.