rename variables in get_all_imports?

[alan-barzilay]

files is parsed and processed to get the list of imported packages, but this list will be contaminated by stdlib packages and local imports which will be removed in other processing steps (lines 165 and 171).

The candidates list is simply a list of local files that could be imported (like an utils.py file) but shouldnt be a part of the requirements file.

If my description is correct, candidates is an awful name. What are they candidates of? also, this would explain why we are adding dir by dir to the list, as I raised in issue #424. Maybe we should rename those objects to something more intuitive.

maybe py_files -> local_files candidates -> local_modules (pretty sure thats the correct nomenclature but we could use a double check)