new distribute_fields_dofs() - support multiple fields
new distribute_fields_dofs() - support multiple fields

- update distribute_field_dofs(), create_task_dof_maps()
- expand DOF components already in distribute_fields_dofs() in multiple fields
  case - governed by use_expand_dofs argument

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