update ContactTerm to return sparse vector and matrix with active DOFs
update ContactTerm to return sparse vector and matrix with active DOFs

- new .call_function(), .eval_real()
- update .function(), .get_fargs()
- TODO: return sparse Gc directly from ccontres

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