added location handling to storage

lib/model/repositories/interfaces/location_repository.dart

@@ -0,0 +1,19 @@
+import '../../location.dart';
+
+abstract class LocationRepository {
+  // Create
+
+  Future<void> createLocation(Location location);
+
+  // Read
+
+  Future<List<Location>> loadLocations();
+
+  // Update
+
+  Future<void> updateLocation(Location location);
+
+  // Delete
+
+  Future<void> deleteLocation(Location location);
+}