bindWhenReady
Binds this content to view whenever the view is ready for content. The content will bind and unbind as this view is attached and detached from the UI.
Returns a closeable that unbinds from the content and stops tracking the ready state.
fun <A : AppService, W : Any> TreehouseContentSource<A>.bindWhenReady(view: TreehouseView<W>, app: TreehouseApp<A>): Closeable