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/src/app/widgets/details.rs

@@ -359,7 +359,7 @@ pub(crate) fn wire_details(ui: &Rc<Ui>) {
 pub(crate) fn show_details(ui: &Rc<Ui>, entry: &DirEntry) {
     ui.details.details_suppress.set(true);
     let d = &ui.details.details;
-    d.icon.set_icon_name(Some(icon_base_for(entry)));
+    d.icon.set_icon_name(Some(icon_for(entry)));
     d.name.set_label(&entry.name);
     d.kind.set_label(&if entry.is_dir {
         gettext("Folder")

crates/pdfs-gui/src/app/widgets/thumbnails.rs

@@ -173,7 +173,7 @@ pub(crate) fn bind_file_thumbnail(
     let fallback_name = if symbolic_fallback {
         format!("{}-symbolic", icon_base_for(entry))
     } else {
-        icon_base_for(entry).to_string()
+        icon_for(entry).to_string()
     };
     fallback.set_icon_name(Some(&fallback_name));
     fallback.set_visible(true);