feat(core,fuse,gui): Proton theme, photos on the map and an opt-in street map

- The Proton accent preference becomes a whole Proton theme that also
  holds against a GTK theme imported from gtk.css; folders get Proton's
  purple folder icon while it is on.
- Places map markers show one of each town's photos with a count, and
  zoomed in on a town every photo sits where it was taken
  (Request::PlaceLocations). Photos taken on one spot are listed in a
  popover. "Show on map" in the photo viewer goes to the Places map.
- The built-in map draws country borders, sea and land in their own
  colours.
- An opt-in street map from OpenFreeMap (vector tiles drawn with cairo,
  cached on disk up to 256 MB), with the OpenStreetMap credit on the map
  and in About.
- Translations for all catalogs; changelog folded into 2.3.0.

crates/pdfs-gui/build.rs

@@ -26,5 +26,6 @@ fn main() {
     println!("cargo:rerun-if-changed=resources/pdfs.gresource.xml");
     println!("cargo:rerun-if-changed=resources/icons");
     println!("cargo:rerun-if-changed=resources/style.css");
+    println!("cargo:rerun-if-changed=resources/proton-theme.css");
     println!("cargo:rerun-if-changed=../../packaging/io.narl.proton-drive-linux.svg");
 }