First output in VTU format

Testing new VTU format.

For now, species information is ALWAYS output in .vtu (to test, this will
    be an independent format in the future).
A .pvd file is produced to do time-series.

Still to implement other outputs (electromagnetic, average,
    collisions...)

Still to implement reading a mesh from .vtu file

src/modules/solver/moduleSolver.f90

@@ -514,6 +514,7 @@ MODULE moduleSolver
       USE moduleSpecies
       USE moduleCompTime
       USE moduleProbe
+      USE moduleMeshOutputVTK !TEMPORARY TO TEST VTK OUTPUT
       IMPLICIT NONE
 
       INTEGER, INTENT(in):: t
@@ -527,6 +528,7 @@ MODULE moduleSolver
 
         CALL outputProbes(t)
         CALL mesh%printOutput(t)
+        CALL printOutputVTK(mesh, t)
         IF (ASSOCIATED(meshForMCC)) CALL meshForMCC%printColl(t)
         CALL mesh%printEM(t)
         WRITE(*, "(5X,A21,I10,A1,I10)") "t/tFinal: ", t, "/", tFinal