Extra scalar fields in IncNS

This MR makes small changes to allow the solution of the advection-diffusion equation for passive scalar fields in the IncNavierStokesSolver.

See merge request !624

Extend ProcessCurve to allow reading coordinates from file

This MR extends the ProcessCurve module of NekMesh to read  the coordinates from a file (in 2D).

The file should be in the .pts format, with `DIM=1` and one field corresponding to the y-coordinate. For example:
``` xml
<?xml version="1.0" encoding="utf-8" ?>
<NEKTAR>
  <POINTS DIM="1" FIELDS="y" >
    0.000000E+00    0.000000E+00
    1.000000E+00    1.000000E+00
  </POINTS>
</NEKTAR>
```

See merge request !628

Conflicts:
	CHANGELOG.md

Avoid reading fld twice in FieldConvert

This MR introduces a small change to avoid loading the fld file twice in FieldConvert. Currently, InputXml imports just the FieldDef to set the expansion, and later InputFld reads the data. However, this is very inefficient, since the whole fld file has to be loaded even if we just want the FieldDef. This MR basically makes InputXml load both the fielddef and the data, and later InputFld just extracts the data.

See merge request !649

Suppress Xxt stats output when running without verbose option

This MR makes small changes to the Xxt solver to output the stats only when we are using the verbose option. Unfortunately, I think it is not possible to suppress the output from gs_setup, which is much more annoying.

See merge request !642

Fix missing package dependency for NekMesh utility.

The MR fixes a missing dependency on libnektar++-nekmeshutils in the nektar++-utilities package.

See merge request !650

Advance tutorials submodule for v4.3.2.

This MR just advances the submodule commit ID for the tutorials.

See merge request !643

Fix instances of MeshConvert in user guide.

This MR includes some minor fixes to the user guide.

See merge request !640

Fix/parallel assert

This MR fixes a bug in the iterative solver whereby the assertion on exceeding the maximum number of iterations is only effected on the root process. This also updates the NekError class to print messages on the root process only, rather than on all processes.

See merge request !636

Modify FC extract checks to allow use without fld

This MR just changes one of the error checks in the extract module of FieldConvert, since it is only required to have an .fld input when using the fldtoboundary option. Without this option, we can use only an .xml file as input, for example to calculate the normals to the surface.

See merge request !638

Fix wss module with partitioned domains

This fixes a bug which prevents the wss module from working in parallel. This happens because in parallel the index from the boundary expansions do not necessarily correspond to the boundary region id.

See merge request !635

FieldConvert module for combining average fields

This MR introduces a new FieldConvert module that combines fields obtained through `FilterAverageFields` or `FilterReynoldsStresses` (the Reynolds stresses are added correctly, what is not possible using only `addfld`).

The number of samples in each field is automatically considered and the total number of samples is stored in the output file, allowing for multiple files from simulations with different numsteps to be combined easily. 

See merge request !620