Get "created by id" (project member)

Summary

Currently, the "members" table has a column "created_by_id". This is not exposed through the API. This issue is to expose that attribute in the API, so we can return all of the users created by a given user.

We can also expose other information about who created the user, including the following:

"created_by": {
  "id": 2,
  "username": "john_doe",
  "name": "John Doe",
  "state": "active",
  "avatar_url": "https://www.gravatar.com/avatar/c2525a7f58ae3776070e44c106c48e15?s=80&d=identicon",
  "web_url": "http://192.168.1.8:3000/root"
},