Draft: Delegate communication of int-valued n1e1 vectors to dofs

The regular n1e1 communication must flip the signs of unknowns to accommodate for inconsistent edge orientations. However, index vectors are not part of the n1e1 function space and thus require special treatment, i.e. no adjustments of signs.

With this change we commit that all non-floating vectors are outside of the n1e1 space and should be communicated without treatments of sign.

Before the only way to output index-vectors was vtkOutput.add( *n1e1Enumerator.getDofs() ). Now we can just write vtkOutput.add( n1e1Enumerator ) like with every other function space.