Tons of pep8 changes

63 commits of pep8 changes, one commit per file/error type.

Remaining pep8 errors in the codebase:

./common/djangoapps/student/views.py:82:15: E712 comparison to False should be 'if cond is False:' or 'if not cond:'
./common/lib/xmodule/xmodule/capa_module.py:462:34: W602 deprecated form of raising exception
./common/lib/xmodule/xmodule/xml_module.py:126:48: E712 comparison to True should be 'if cond is True:' or 'if cond:'
./common/lib/xmodule/xmodule/modulestore/xml_importer.py:509:76: E712 comparison to True should be 'if cond is True:' or 'if cond:'
./common/lib/capa/capa/responsetypes.py:863:36: W602 deprecated form of raising exception
./common/lib/capa/capa/responsetypes.py:1227:28: W602 deprecated form of raising exception