[NP-6979] Make it possible to generate Null implementors

[KernelDeimos]

Allows convenient generation of no-op implementors of interfaces. For example, the code snippet below creates Loader, ProxyLoader, and NullLoader.

foam.INTERFACE({
  package: 'foam.u2.wizard.data',
  name: 'Loader',
  proxy: true,
  null: true,

  methods: [
    {
      name: 'load',
      async: true
    }
  ]
})

[kgrgreer]

Are we using this anywhere? If not, if it could be self-contained in it's own file (as a refinement on interface) and then don't include it in the standard POM so we don't include it if not needed.

[KernelDeimos]

Are we using this anywhere? If not, if it could be self-contained in it's own file (as a refinement on interface) and then don't include it in the standard POM so we don't include it if not needed.

This will be used by WAO and the new Loader,Saver,Canceler interfaces in foam.u2.wizard