Finishing implementation of vtu mesh format

I have tested all geometries and cases and all seem to work perfectly
with .vtu meshes.

Input and output works great, starting from a previous case also works.
Everything I was able to test is okay.

Still, what I want to do is to change a few things in the output (e.g.,
    change OUTPUT prefix to Step) and try to improve reading gmsh meshes
to make them more compact as vtu is now.

src/modules/mesh/inout/vtu/moduleMeshInputVTU.f90

@@ -359,7 +359,7 @@ MODULE moduleMeshInputVTU
             END IF
 
           CASE(1)
-            IF (types(n) == 3) THEN
+            IF (types(n) == 1) THEN
               e = e + 1
               ALLOCATE(p(1:1))
               p(1) = connectivity(offsets(n))