Add collection delete to the new API.

Example:
```java
client.delete("someCollection").execute();
```

Note:
* I've ignored all old test cases and introduced `junit-quickcheck`
* The hardcoded API key will be factored out (and deleted from Orchestrate) as I add more test cases and combine some of their shared properties.
* The sample set size used with the quickcheck test cases is set to `10` for each test case because I tried it with the default (`100`) and it was taking over 2 minutes to run these two test theories. I may make this value configurable in the future.

@housejester ping