Add error handling screen to view station page

lib/pages/station_arrdep_page/view_station/view_station.dart

@@ -51,6 +51,8 @@ abstract class ViewStationPageShared extends StatelessWidget {
   static const departsTo = 'Pleacă către';
   static const departedTo = 'A plecat către';
   static const cancelledDeparture = 'Anulat - către';
+  static const errorText = 'A apărut o eroare';
+  static const retryText = 'Reîncearcă';
 
   final ViewStationPageTab tab;
   final void Function(ViewStationPageTab) setTab;

lib/pages/station_arrdep_page/view_station/view_station_material.dart

@@ -27,7 +27,41 @@ class ViewStationPageMaterial extends ViewStationPageShared {
       body: snapshot.state == RefreshFutureBuilderState.waiting 
         ? const Loading(text: ViewStationPageShared.loadingText,) 
         : snapshot.state == RefreshFutureBuilderState.error
-        ? Container()
+        ? Padding(
+          padding: const EdgeInsets.all(8.0),
+          child: Center(
+            child: Column(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                const Icon(
+                  Icons.error_outline,
+                  size: 32,
+                  color: Colors.red,
+                ),
+                const Text(
+                  ViewStationPageShared.errorText,
+                  style: TextStyle(
+                    inherit: true,
+                    fontSize: 32,
+                  ),
+                ),
+                Text(
+                  snapshot.error.toString(),
+                  style: Theme.of(context).textTheme.bodySmall,
+                ),
+                Padding(
+                  padding: const EdgeInsets.all(8.0),
+                  child: ElevatedButton(
+                    onPressed: () {
+                      refresh();
+                    },
+                    child: const Text(ViewStationPageShared.retryText),
+                  ),
+                ),
+              ],
+            ),
+          ),
+        )
         : CustomScrollView(
           slivers: [
             SliverToBoxAdapter(child: SafeArea(left: false, bottom: false, right: false,child: Container(),),),