Adding advanced scoping functionality

So, here's the pull request for the scoping functionality as explained in #94.

As I said, I had to alter the codebase more than I initially thought I had to. But I quickly figured I had to dig into  the creation of channels and the publishing of actions to accomplish my goal. I introduced a couple new classes and moved some logic around to wrap it in a clean way.

I left most of the existing tests untouched. Just had to rewrite ```model_test.rb``` to fit and cover the new, more complex callback functionality of the ```Model``` class.

Hope you understand what I was doing. ;)