PField does not accept the VTK output provided by ParaView

Currently PFields assumes that the "LOOKUP_TABLE" block of a *.vtk file looks like:
```
POINT_DATA 256
SCALARS n double 1
LOOKUP_TABLE default
```

However, an exported *.vtk file from ParaView looks like:
```
POINT_DATA 256
FIELD FieldData 1
c 1 256 double
```

This should be a relatively straightforward fix.