How can I configure Scalatra (sbt) to find the webapp folder in a different source folder than "main"

Question

By default, Scalatra expects the "webapp" directory to be at src/main/webapp. How could that be changed to src/web/webapp?

In my application, I would like to have the following folder structure:

src
    web
        scala
        resource
        webapp
    main
        scala
        resource
    test
        scala
        resource

1. What do I need to have on my sbt to make the web folder become a source folder?
2. How do I make Scalatra understand that the "webapp" folder is not on main but on web folder?