define arg_shapes attribute of ContactPlaneTerm, update docstring
define arg_shapes attribute of ContactPlaneTerm, update docstring

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