Issue #231

Pull request for issue #231. Also, I've done a todo from RtDeployKeysTest.java:89-93, because I needed the get() method:
```java
     * @todo #119 RtDepoyKeys should be able to get a single key.
     *  Let's implement a test here and a method get() of RtDeployKeys.
     *  The method should fetch a single deploy key.
     *  See how it's done in other classes, using Rexsl request/response.
     *  When done, remove this puzzle and Ignore annotation from the method.
```