Add preview stack

lib/redux/app/app_actions.dart

@@ -171,6 +171,8 @@ class PreviewEntity {
 
 class ClearPreviewStack {}
 
+class PopPreviewStack {}
+
 class ClearData {}
 
 class RefreshDataFailure implements StopLoading {

lib/redux/ui/ui_reducer.dart

@@ -298,4 +298,8 @@ Reducer<BuiltList<EntityType>> previewStackReducer = combineReducers([
       (previewStack, action) {
     return BuiltList(<EntityType>[]);
   }),
+  TypedReducer<BuiltList<EntityType>, PopPreviewStack>((previewStack, action) {
+    return BuiltList(
+        <EntityType>[...previewStack.sublist(0, previewStack.length - 1)]);
+  }),
 ]);

lib/ui/app/view_scaffold.dart

@@ -52,7 +52,7 @@ class ViewScaffold extends StatelessWidget {
     }
 
     Widget leading;
-    if (!isMobile(context)) {
+    if (isDesktop(context)) {
       if ((isFilter ?? false) &&
           entity.entityType == state.uiState.filterEntityType) {
         leading = IconButton(
@@ -61,6 +61,10 @@ class ViewScaffold extends StatelessWidget {
             store.dispatch(UpdateUserPreferences(showFilterSidebar: false));
           },
         );
+      } else if (state.uiState.previewStack.isNotEmpty) {
+        leading = IconButton(
+            icon: Icon(Icons.arrow_back),
+            onPressed: () => store.dispatch(PopPreviewStack()));
       } else if (isSettings) {
         leading = IconButton(
           icon: Icon(Icons.arrow_back),