Adding support for ActivateAttribute via IControllerActivator

This mechanism replaces code in Inject that activated properties
by looking them up by names.

First draft as a POC. Tests will come in later iterations.
@yishaigalatzer This was the change I mentioned earlier in the day. In Mvc 5, IControllerFactory took a string controllerName and turned that into an IController instance. In our case, the controller factory really is a wrapper around ITypeActivator. I'm not sure it makes sense for us to continue having that.