Update gallery, fix Cupertino fonts by using GoogleSans instead (#155)

* Update gallery, fix Cupertino fonts

Cupertino fonts fixed by using GoogleSans instead

* remove BUILD.gn

* remove ios and android dirs from web/gallery

* remove meta/flutter_gallery.cmx

* revert provider_shopper/pubspec.lock

* remove gallery's test and tool directories

* update web/gallery README

web/gallery/lib/demo/fortnightly/fortnightly.dart

@@ -139,7 +139,7 @@ class FruitPage extends StatelessWidget {
                       padding: const EdgeInsets.symmetric(vertical: 16),
                       child: Row(
                         children: <Widget>[
-                          CircleAvatar(
+                          const CircleAvatar(
                             backgroundImage: ExactAssetImage(
                               'people/square/trevor.png',
                               package: 'flutter_gallery_assets',