move README content to Makefile

It's not necessary to copy commands from README anymore. Just use
'make source_list', 'make template' or 'make locales'.

fix pylint warning '(global-variable-not-assigned) Using global for 'X' but no assignment is done'

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