[pylint] more work on the pylint support
* uniformize usage of ClassDef and simplify related import
* don't insert in the ast a python function but an astroid representation of that function
* ignore __pkginfo__ file
* drop attr-rgx, variable-rgx and argument-rgx, put the name in good-names instead
* drop additional-builtins
* add cell_call to the list of methods for which we don't want 'abstract-method'
