Fix bug 1045036 - Promisify webmaker-user-client

This is what I get when I log out `userClient`.

```javascript
{ endpoint: 'http://testuser:password@localhost:3000',
  returnUser: [Function],
  returnUsers: [Function],
  get:
   { byId: [Function: getById],
     byEmail: [Function: getByEmail],
     byUsername: [Function: getByEmail],
     byIds: [Function: getByIds],
     byEmails: [Function: getByEmails],
     byUsernames: [Function: getByUsernames] },
  update:
   { byEmail: [Function: updateByEmail],
     byId: [Function: updateById],
     byUsername: [Function: updateByUsername] },
  returnUserAsync: { [Function: returnUserAsync] __isPromisified__: true },
  returnUsersAsync: { [Function: returnUsersAsync] __isPromisified__: true } }
```

Doesn't seem to do sub-object traversal...