Add costume dataURI to costumes from storage (#517)

* Add costume dataURI to costumes from storage

Towards #515, LLK/scratch-gui#279

* Fix tests

* Load costumes incrementally

Some of our tests assume that at least some of our costume data is available before the costume data is loaded. So, provide as much costume data as is available.

* Remove unnecessary filter for null costumes

Resolved when we updated to load costumes incrementally.

/ht @cwillisf

test/integration/complex.js

@@ -40,14 +40,17 @@ test('complex', function (t) {
                 rotationStyle: 'all around',
                 visible: true
             });
-            vm.addCostume({
-                costumeName: 'costume1',
-                baseLayerID: 0,
-                baseLayerMD5: 'f9a1c175dbe2e5dee472858dd30d16bb.svg',
-                bitmapResolution: 1,
-                rotationCenterX: 47,
-                rotationCenterY: 55
-            });
+            vm.addCostume(
+                'f9a1c175dbe2e5dee472858dd30d16bb.svg',
+                {
+                    costumeName: 'costume1',
+                    baseLayerID: 0,
+                    baseLayerMD5: 'f9a1c175dbe2e5dee472858dd30d16bb.svg',
+                    bitmapResolution: 1,
+                    rotationCenterX: 47,
+                    rotationCenterY: 55
+                }
+            );
         }
     });
 
@@ -73,14 +76,17 @@ test('complex', function (t) {
         vm.addSprite2(sprite);
 
         // Add backdrop
-        vm.addBackdrop({
-            costumeName: 'baseball-field',
-            baseLayerID: 26,
-            baseLayerMD5: '6b3d87ba2a7f89be703163b6c1d4c964.png',
-            bitmapResolution: 2,
-            rotationCenterX: 480,
-            rotationCenterY: 360
-        });
+        vm.addBackdrop(
+            '6b3d87ba2a7f89be703163b6c1d4c964.png',
+            {
+                costumeName: 'baseball-field',
+                baseLayerID: 26,
+                baseLayerMD5: '6b3d87ba2a7f89be703163b6c1d4c964.png',
+                bitmapResolution: 2,
+                rotationCenterX: 480,
+                rotationCenterY: 360
+            }
+        );
     });
 
     // After two seconds, get playground data and stop