Intial commit mid-side nodes branch

This branch tries to handle situations when mid-side nodes are left out from writing to VTK file. Node numbers, coordinates, results, elements connectivity and all you can imaginge has to be handled accordingly.
VTK cell type recognition at reading .ELEM file

A corresponding cell type gets written to .vtk file (recognition logic currently supports the QUAD and HEXAHEDRON cell types).
added vector field
added Paraview state .pvsm and .vtk
read_dot_node() saves nodes contained in elemnts connectivity list

This allows to filter out unnecessary nodes while reading the .NODE file (e.g., mid-side nodes).
This commit also takes aboard paraview states with pretty glyphs for critical planes and normals visualization