Added _setup(), removed destroy(), added add/remove quicktest

_setup() is called during anchor() if the Component's element hasn't
been created yet. Subclasses override _setup() to add additional
elements to the DOM.

The implementation of destroy() can be somewhat tricky (Renderers
may need to disconnect from their data carefully, etc), so that has
been deferred until later.

Added a quicktest for testing addition/removal of Components.