Add Init event to containers

[intentor]

To allow container and extensions initilization, the container should have a Init() method, which can be used to populate cache and initialize internal bindings.

Using ContextRoot, the method is called automatically during initialization. Manually, it should be called after all bindings and container settings have been added.

Additionally, the event can be used on the CommanderExtension to perform late bindings, allowing to remove the current temporal coupling that exists between command registration and bindinds.