Analyze Scripts not in a Package

Currently we only analyze scripts that are part of a setup.py described package. This PR adds extra code to the scanner that will bundle up all unaccounted scripts, and put them in a source unit of their own.
if you made the SourceUnit's directory be the directory that contains the requirements.txt file (if it exists), then you might be able to get this for free; I forget whether the existing Python dependency code requires a setup.py. Even if it does, though, I think it could easily be modified to just ignore this constraint, since it also checks the requirements.txt.

I think the best way to implement this is to make the current python dependency code generic, w/o introducing a second code path here if possible.