Fixes #687

Tidied people list, now displaying joined at date

server/presenters/__snapshots__/user.test.js.snap

@@ -3,6 +3,7 @@
 exports[`presents a user 1`] = `
 Object {
   "avatarUrl": "http://example.com/avatar.png",
+  "createdAt": undefined,
   "id": "123",
   "name": "Test User",
   "username": "testuser",
@@ -12,6 +13,7 @@ Object {
 exports[`presents a user without slack data 1`] = `
 Object {
   "avatarUrl": null,
+  "createdAt": undefined,
   "id": "123",
   "name": "Test User",
   "username": "testuser",

server/presenters/user.js

@@ -21,6 +21,7 @@ export default (
 ): UserPresentation => {
   const userData = {};
   userData.id = user.id;
+  userData.createdAt = user.createdAt;
   userData.username = user.username;
   userData.name = user.name;
   userData.avatarUrl =