MODE-2259 Fixed the WebApp handlers.

Since the requirement is to be able to deploy WARs from within our EAP subsystem, the only way I was able to figure out how to do this is via the `DeploymentAddHandler` which only works in the `MODEL` stage.

The solution was to check in our handlers the `requiresRuntime(context)` and only perform the model change & invoke the handler for a "NORMAL" server.
IMO the value of the assert is more clarity, but it's fine if you don't want to add it. I guess right now, the only thing I am asking for is better comments.