TimeGovernor::view() use just Msg message type

- in fact it is not debugging mesage, MsgDbg should be used just
   through DBGMSG maccro, otherwise it could be interchanged with
   debugging output
- add conditional call of the view function where it is used
FieldElementwise - add constructor from std::vector
FieldSet - check for duplicit addition

- operator += check if the field is already present in the field set
- internal method field_by_name
- add safety assert in field_impl
OutputTime can be constructed an all processors

- remove some rank tests so that we allow construction of OutputTime
  classes, but open the file and perform output only on master process
Fix output for DarcyFlow

- support standard output fields and error fields
- support output of subdomain indices
- some simplifications
- fix destructor