Provide a method to dispose an Aurelia instance

[sylvain-hamel]

The framework should provide a method to shut down / dispose an Aurelia application instance.

Calling aurelia.dispose() would dispose all objects / event listeners created by Aurelia including:

• unbind/detach views
• release instances held by containers
• dispose all EventAggregators and bindings to release subscribers
• dispose / deactivate the router(s)
• null out the aurelia.container property and the aurelia.loader properties (as recommended by @EisenbergEffect in a private Gitter chat about this)