Coding Conventions for Python Code

Apply coding style conventions except error E501 (line too long) using pep8.

Remove unused imports using pylama.

Some errors still remain :

• E741 ambiguous variable name 'l' (HelperClass.py, TestVLP.py, TestVLP2.py)
• C901 'VlpProblem.to_file' is too complex (41) (HelperClass.py)
• E0602 undefined name 'block_diag' (HelperClass.py)
• E0602 undefined name 'eye' (HelperClass.py)

mentioned in commit ff22ed1f

merged