add widget for wrapping images that can be fullscreened

lib/widgets/fullscreenable_image.dart

@@ -0,0 +1,25 @@
+import 'package:flutter/material.dart';
+
+import '../pages/media_view.dart';
+
+class FullscreenableImage extends StatelessWidget {
+  final String url;
+  final Widget child;
+
+  const FullscreenableImage({Key key, this.url, this.child}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return InkWell(
+      onTap: () {
+        Navigator.of(context).push(MaterialPageRoute(
+          builder: (context) => MediaViewPage(url),
+        ));
+      },
+      child: Hero(
+        tag: url,
+        child: child,
+      ),
+    );
+  }
+}