Refactor VectorFieldVTKWriter and VectorFieldGnuplotWriter
The VectorFieldVTKWriter and VectorFieldGnuplotWriter classes should be refactored analogically to MeshFunctionVTKWriter and MeshFunctionGnuplotWriter.
Edited by Jakub Klinkovský
The VectorFieldVTKWriter and VectorFieldGnuplotWriter classes should be refactored analogically to MeshFunctionVTKWriter and MeshFunctionGnuplotWriter.