Implemented TestManager.compare_pys(path_1, path_2).

The method checks two see if two Python files compare equal.

The method discards blank lines and trims whitespace.

The method then performs a line by line comparison.

So the method is basically equivalent to diff with a little additional
flexibility for whitespace.

These three static methods all implement the same interface:

    * TestManager.compare_pys(path_1, path_2)
    * TestManager.compare_lys(path_2, path_2)
    * TestManager.compare_pdfs(path_2, path_2)
Implemented TestManager.compare_files(path_1, path_2).

The method generalizes ...

    * TestManager.compare_lys(path_1, path_2)
    * TestManager.compare_pdfs(path_1, path_2)
    * TestManager.compare_pys(path_1, path_2)

... and provides an all-purpose tool for artifact comparison in the IDE.