Increase Coverage

Additional and better tests to increase test coverage to approximately 96%.

```
Name                       Stmts   Miss  Cover   Missing
--------------------------------------------------------
createsend                    11      0   100%   
createsend.administrator      26      2    92%   3-4
createsend.campaign           65      2    97%   3-4
createsend.client             79      2    97%   3-4
createsend.createsend        157      8    95%   153-161
createsend.list               87      2    98%   4-5
createsend.person             27      2    93%   3-4
createsend.segment            34      2    94%   3-4
createsend.subscriber         43      2    95%   3-4
createsend.template           23      2    91%   3-4
createsend.utils              36      2    94%   4-5
--------------------------------------------------------
TOTAL                        588     26    96%   
----------------------------------------------------------------------
Ran 275 tests in 0.148s
```