New: do the simple thing for module loading

This PR replaces the old naming scheme for Prose module classes with a much simpler one:

* $st->verbNoun() gets translated to `return new VerbNoun($st)`

It allows future modules to introduce any new verbs they want with no further changes required to Storyplayer.  No existing stories will break; only existing additional modules (such as our internal ms-lib-prose ones) will need renaming.

Namespaces are not changed by this PR at all.