Fix continuation-related PEP8 issues

This changeset resolves 105 PEP8 issues: It addresses the following
whitespace-related PEP8 violations:
- E121 continuation line indentation is not a multiple of four
- E122 continuation line missing indentation or outdented
- E123 closing bracket does not match indentation of opening bracket's line
- E124 closing bracket does not match visual indentation
- E125 continuation line does not distinguish itself from next logical line
- E126 continuation line over-indented for hanging indent
- E127 continuation line over-indented for visual indent
- E128 continuation line under-indented for visual indent

The PEP8 threshold has been lowered to 15.