The directive automates management of components in RouterOutletComponentBus.
Outlets marked with publishComponent will publish and unpublish components automatically to the bus.
PublishComponentDirective reads the name of the outlet, then listens to the outlet's activate and deactivate events.
When the outlet activates a component, the directive publishes it to the bus service along with the outlet's name.
When the outlet deactivates a component, the directive publishes a null value along with the outlet's name.
When the outlet is destroyed (i.e. removed from the DOM), the directive unpublishes the component from the bus service.
See RouterOutletComponentBus for instructions.