extensions extended by unit-vector/-matrix; FixVec,Vector and Matrix corrected and extended; lots of other changes

merge from linearAlg-branch. my parallelization needed a slightly more general linear solver interface and uses the pvd-naming scheme from the petsc-parallelization

  overwritten
Others: Add each DOFVector by construction to the list of interchange vectors
and remove them by destruction
If you dont want to exchange the vector, set the boolean synch to false