Added set/get to display stis, atoms

Hi @cosmoharrigan, I thought we could discuss on this pull request specifically how to move forward regarding the attention interface.
I'm not sure yet how the AttentionalFocus is composed that is returned by the call to the REST API with ```atoms?filterBy=af```: As all STIs are 0, there should be nothing in the AF. How is the AF defined here?
You can print the result in your client application if you wish to, rather than making it always print as part of the library.