use actual reference mapping data in get_einsum_ops()
use actual reference mapping data in get_einsum_ops()

- do not store the mapping data in ExpressionArg
- update ExpressionArg.from_term_arg(), .get_dofs()
- new ExpressionArg.get_bf()
- update ETermBase.make_function()

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