added search functionality

lib/view/locationSearch.dart

@@ -0,0 +1,60 @@
+import 'package:flutter/material.dart';
+import 'package:latlong2/latlong.dart';
+import 'package:osm_nominatim/osm_nominatim.dart';
+
+class LocationSearchDelegate extends SearchDelegate<LatLng?> {
+  @override
+  List<Widget>? buildActions(BuildContext context) {
+    return [
+      IconButton(
+        icon: const Icon(Icons.clear),
+        onPressed: () => query = '',
+      )
+    ];
+  }
+
+  @override
+  Widget? buildLeading(BuildContext context) {
+    return IconButton(
+      icon: const Icon(Icons.arrow_back),
+      onPressed: () => close(context, null),
+    );
+  }
+
+  @override
+  Widget buildResults(BuildContext context) {
+    return FutureBuilder<List<Place>>(
+      future: query.isEmpty ? Future.value([]) : Nominatim.searchByName(
+          query: query,
+          limit: 10,
+          language: 'de',
+          // https://gist.github.com/graydon/11198540#file-country-bounding-boxes-py-L45
+          viewBox: ViewBox(54.983104153, 15.0169958839, 47.3024876979, 5.98865807458)
+      ),
+      builder: (BuildContext context, AsyncSnapshot<List<Place>> snapshot) {
+        switch (snapshot.connectionState) {
+          case ConnectionState.waiting:
+            return const Center(child: CircularProgressIndicator());
+          case ConnectionState.active:
+          case ConnectionState.none:
+          case ConnectionState.done:
+            return ListView.builder(
+              itemCount: snapshot.data?.length ?? 0,
+              itemBuilder: (context, index) {
+                Place place = snapshot.data![index];
+                return ListTile(
+                  title: Text(place.displayName),
+                  onTap: () => close(context, LatLng(place.lat, place.lon)),
+                );
+              },
+            );
+        }
+      },
+    );
+  }
+
+  @override
+  Widget buildSuggestions(BuildContext context) {
+    return buildResults(context);
+  }
+}