update FEDomain__init__() for CMesh in Mesh and no element groups
update FEDomain__init__() for CMesh in Mesh and no element groups

- remove .setup_groups(), .iter_groups(), .get_cell_offsets()
- remove .groups, .mat_ids_to_i_gs, .cell_offsets attributes

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