allow Region.from_vertices() to select groups (add igs argument)
allow Region.from_vertices() to select groups (add igs argument)

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