Added CDN thumb generation.

client/src/utils/DocHelpers.js

@@ -0,0 +1,13 @@
+export const generateCdnThumb = key => {
+  const imageRequest = JSON.stringify({
+    bucket: process.env.REACT_APP_S3_BUCKET,
+    key: key,
+    edits: {
+      resize: {
+        height: 100,
+        width: 100
+      }
+    }
+  });
+  return `${process.env.REACT_APP_S3_CDN}/${btoa(imageRequest)}`;
+};