Add support for Gmsh high-order output

This MR primarily adds support for Gmsh output at arbitrarily high-order for quads, hexes, triangles and tetrahedra, and up to order 4 output for prisms.

See merge request !679

Add checks to make sure npz is consistent with HomModesZ

This MR just introduces a couple of ASSERTL0 to make sure the partitioning in z for homogeneous simulations leads to an even number of planes per process.

See merge request !666

HDF5 support for parallel output

This MR adds support for HDF5 output format as an alternative to our existing XML-based format thanks to the hard work of @mrbareford and @rupert.nash! The following changes have been incorporated as part of this work:

- Move `FieldIO` to a factory format, with `FieldIOXml` for XML output and `FieldIOHdf5` for HDF5 output.
- Default output format is XML but can be switched to HDF5 by setting the `IOFormat` SOLVERINFO tag, or the `--io-format` command line argument -- the argument will override the XML file.
- The MPI communicator has been templated to allow a wider range of data types to be sent/received, and a couple of new functions have been added (broadcast, splitting of communicator on bool, ...)
- Boundary conditions are now equipped with their own communicator so that we can read HDF5 on a subset of processors.
- Lots of Doxygen added for both formats
- FieldConvert can also convert between formats:

```
FieldConvert in.fld out.fld:fld:format=Hdf5
```

See merge request !615

Fix prism output up to order 4 (but no higher right now), fix the use of face IDs for generic 3D elements

New FC module to add composite ID as a field

This MR adds a FieldConvert module for adding the composite ID of the element to the output field. This is useful when many composites are present in the domain and need to be identified.

See merge request !674

EquispacedOutput in 1D

This MR extends the `equispacedoutput` module of FieldConvert to 1D and 2DH1D expansions (1D only for .vtu).

It also makes some changes to allow `interppoints` and `equispacedoutput` to output to .pts files.

See merge request !613

Update NekMesh linearise module

This MR updates the linearise if invalid command so that all element and curvature types can be processed. Additionally, it will recursively sweep through neighbours so that the module does not need to be run more than once to get rid of all invalid elements.

See merge request !659

Add projection equation system to ADRSolver

This MR adds a projection operator to the ADRSolver, which can be used to impose C^0 connectivity on an input forcing field and is useful in e.g. the creation of boundary conditions on complex geometries.

See merge request !675