update Region for no element groups
update Region for no element groups

- update .__init__(), .set_kind(), .update_shape(), .get_entities(),
  .get_cells(), .get_facet_indices(), .setup_mirror_region(),
  .get_mirror_region(), .get_n_cells()
- remove .igs property, ._igs, .ig_map, .ig_map_i attributes
- remove .get_vertices(), .get_edges(), .get_faces(), .get_facets(),
  .iter_cells(), .get_cell_offsets()

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