fix pylint error '(function-redefined) method already defined'

fix pylint warning '(unreachable) Unreachable code'

fix pylint warning (bad-indentation) Bad indentation. Found X spaces, expected Y

fix pylint warning '(pointless-string-statement) String statement has no effect'

Python doesn't support docstring for variables directly. Where
appropriate Sphinx style for docstrings for variables is used
'#: some-docstring'

fix error __init__ method from base class is not called

fix more than one statement on a single line

fix ungrouped imports from package X

fix unnecessary lambda and enable corresponding pylint check

fix wrong-import-order. first standard modules are imported, then others

fix (old-style-class) Old-style class defined error for most parts of
the code

only PyJS code is left, because it does some fancy tricks and can't be
easily fixed. So far PyJS doesn't support Python3 anyway.