Support non-recursive scanning of a rules path

Slide: https://docs.google.com/presentation/d/1ijAWBKBJi90j6eCjHdkk-y22gGjzJZ2J7XVQcZejaiI/edit#slide=id.g1d8fe0edb4_0_38

Provide a way to indicate that a directory should not be scanned recursively. This will require a few changes:

1. The web ui must scan the directory itself, get a list of files (either recursive or non-recursive) and use this list to load the rules for display as well as to know which files to pass into windup-core at analysis time.

2. The registration should still function as a path registration, rather than as an import. New files in the folder should automatically be used.