REST related mods that use web.xml

merge changes required to load a web.xml and application named in the web.xml. Currently web.xml is hardcoded in ServingLayer.java but should probably be specified via a config param.
Ah, so this will work if we remove the `@ApplicationPath` annotations, but still explicitly name an Application as a servlet?

Does this hold true even without web.xml?

Although we should use web.xml for as much as possible, in this case I am not sure we can configure the Application this way because it requires hard-coding an Application class, whereas we want that to come from the configuration. 

Hm, I wonder if we can use web.xml after all then. Certainly it can hold all the other config but this one is tricky. Maybe we can chat about this one.