fix(image): Popover should appear above preview controls (#635)

Author: Conrad Chan

src/image/ImageAnnotator.scss

@@ -10,4 +10,11 @@
     .ba-is-drawing {
         user-select: none; // Prevent visible selection highlight
     }
+
+    // Raise the rendering order to override the stacking context created by the
+    // transform applied to each of the managers' react mount element to account for
+    // rotation
+    .ba-Layer--popup {
+        z-index: 1;
+    }
 }