Add region management

This adds region management: the user can manage a list of available regions
and for each channel pick a region from that list to apply to messages.

Region discovery from nearby repeaters will be done in a separate PR.

This is a part of the work needed for #120.

lib/l10n/app_localizations_de.dart

@@ -338,6 +338,36 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get settings_radioSettingsUpdated => 'Funkparameter aktualisiert';
 
+  @override
+  String get settings_regionSettings => 'Regionen';
+
+  @override
+  String get settings_regionSettingsSubtitle =>
+      'Gespeicherte Regionen verwalten';
+
+  @override
+  String get settings_regionManagement_screenTitle => 'Regions-Verwaltung';
+
+  @override
+  String get settings_regionNameHint => 'Regions-Namen eingeben';
+
+  @override
+  String get settings_regionAddRegion => 'Region hinzufügen';
+
+  @override
+  String get settings_regionName => 'Regions-Name';
+
+  @override
+  String get settings_regionDeleted => 'Region entfernt';
+
+  @override
+  String get settings_deleteRegion => 'Region entfernen';
+
+  @override
+  String settings_deleteRegionConfirm(String region) {
+    return 'Region \"$region\" aus der Liste entfernen?';
+  }
+
   @override
   String get settings_location => 'Ort';
 
@@ -1235,6 +1265,20 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get channels_hashtagHint => 'z.B. #team';
 
+  @override
+  String channels_regionSetTo(String region) {
+    return 'Region: $region';
+  }
+
+  @override
+  String get channels_regionNotSet => 'Region: keine';
+
+  @override
+  String get channels_regionSelect_Title => 'Region auswählen';
+
+  @override
+  String get channels_clearRegion => 'Region zurücksetzen';
+
   @override
   String get chat_noMessages => 'Noch keine Nachrichten.';