new ExpressionBuilder.make_psg(), update .add_virtual_arg(), .add_state_arg()
new ExpressionBuilder.make_psg(), update .add_virtual_arg(), .add_state_arg()

- ELinearElasticTerm works also in residual mode (but still WIP)

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