Make a valid selection for each stage

This selection object can be used for ExtractClosureAnalyzer.

See #56.
Remove testing code

We had some old testing code here that we can now safely remove.

See #56.
[BROKEN] First step into trying to analyze a bunch of stages at once

Previously, ExtractClosure will only do one closure at a time. Now
we are expanding it to handle multiple closures (stages) at a time.

Obviously code will be broken at this point.

See #56.