SimpleController can be used as a controller according to the model-view-controller (M-V-C) paradigm. It provides an IdentityDictionary of actions, which are called whenever the attached model sends a notification by calling changed.
Creates a SimpleController instance with the model to be observed.
| model | An object of any class | 
| what | Register an action, which is called when the model invokes changed(what, moreArgs). | 
| action | Action to register. | 
Remove a registered action.
| (action) | Action to remove |