update IGMapping for nurbs patch other than domain.nurbs
update IGMapping for nurbs patch other than domain.nurbs

- update IGMapping.__init__() - new nurbs argument
- update docstring

RexFuzzle/sfepy,RexFuzzle/sfepy,BubuLK/sfepy,rc/sfepy,BubuLK/sfepy,RexFuzzle/sfepy,vlukes/sfepy,lokik/sfepy,vlukes/sfepy,rc/sfepy,lokik/sfepy,sfepy/sfepy,rc/sfepy,lokik/sfepy,sfepy/sfepy,sfepy/sfepy,vlukes/sfepy,lokik/sfepy,RexFuzzle/sfepy,BubuLK/sfepy