Make the CLI clever script work + tests

The CLI clever is broken.
```
$ bin/clever district all -k DEMO_KEY
Running the equivalent of:
--
curl https://api.clever.com/v1.1/districts -H "Authorization: Basic REVNT19LRVk="
--
Traceback (most recent call last):
  File "bin/clever", line 211, in <module>
    sys.exit(main())
  File "bin/clever", line 208, in main
    return method(params)
  File "bin/clever", line 83, in all
    self.logged_curl('get', url, params)
  File "bin/clever", line 30, in logged_curl
    rbody, rcode, _ = clever.APIRequestor().request_raw(method, url, dict_params)
  File "bin/../clever/__init__.py", line 247, in request_raw
    raise AuthenticationError('Must provide either api_key or token auth. {}'.format(my_auth))
clever.AuthenticationError: Must provide either api_key or token auth. {}
```
These commits fix the problem and add two tests.