discontinuous: make DiscontinuousField use DiscontinuousApproximation
discontinuous: make DiscontinuousField use DiscontinuousApproximation

- new DiscontinuousField.setup_approximations(), .setup_coors()

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