PEP8: indentation fixes

[neteler]

(Trivial) indentation fixes, including:

• E121 continuation line under-indented for hanging indent
• E122 continuation line missing indentation or outdented
• E123 closing bracket does not match indentation of opening bracket's line
• E125 continuation line with same indent as next logical line
• E128 continuation line under-indented for visual indent
• E131 continuation line unaligned for hanging indent
• E202 whitespace before ')'
• E211 whitespace before '('
• E221 multiple spaces before operator
• E225 missing whitespace around operator
• E261 at least two spaces before inline comment
• E271 multiple spaces after keyword
• E302 expected 2 blank lines, found 1
• E303 too many blank lines (2)
• E305 expected 2 blank lines after class or function definition, found 1

Needed for new GitHub action "flake8", see #140