Fix whitespace-related PEP8 issues

This changeset resolves 58 PEP8 issues: It addresses the following
whitespace-related PEP8 violations:
- W291 trailing whitespace
- E261 at least two spaces before inline comment
- E251 unexpected spaces around keyword / parameter equals
- E241 multiple spaces after ','
- E231 missing whitespace after '[:,]'
- E226 missing whitespace around arithmetic operator
- E225 missing whitespace around operator
- E222 multiple spaces after operator
- E221 multiple spaces before operator
- E211 whitespace before '('
- E203 whitespace before ':'
- E202 whitespace before '}'
- E201 whitespace after '{'

The PEP8 threshold has been lowered to 150.