Show all lightbox controls in style guide

ts/components/Lightbox.md

@@ -1,5 +1,10 @@
 ```js
 <div style={{position: 'relative', width: '100%', height: 500}}>
-  <Lightbox imageURL="https://placekitten.com/800/600"/>
+  <Lightbox
+    imageURL="https://placekitten.com/800/600"
+    shouldShowSaveAsButton={true}
+    shouldShowNextButton={true}
+    shouldShowPreviousButton={true}
+  />
 </div>
 ```