New React component: Message

Also: Use react to render contects on the 'show group members' screen

ts/styleguide/StyleGuideUtil.ts

@@ -35,6 +35,9 @@ const txtObjectUrl = makeObjectUrl(txt, 'text/plain');
 // @ts-ignore
 import mp4 from '../../fixtures/pixabay-Soap-Bubble-7141.mp4';
 const mp4ObjectUrl = makeObjectUrl(mp4, 'video/mp4');
+// @ts-ignore
+import png from '../../fixtures/freepngs-2cd43b_bed7d1327e88454487397574d87b64dc_mv2.png';
+const pngObjectUrl = makeObjectUrl(png, 'image/png');
 
 // @ts-ignore
 import landscapeGreen from '../../fixtures/1000x50-green.jpeg';
@@ -70,6 +73,8 @@ export {
   gifObjectUrl,
   mp4,
   mp4ObjectUrl,
+  png,
+  pngObjectUrl,
   txt,
   txtObjectUrl,
   landscapeGreen,