Expansion from restart file and improved partitioning

This MR makes two changes which might be useful for simulations with variable polynomial order:
- Allow the expansions to be loaded directly from the field definitions in a restart file (issue #14), using:

```xml
<EXPANSIONS>
     <F FILE="restartfile.fld" />
</EXPANSIONS>
```
This is useful when using DriverAdaptive, since in that case the final distribution of polynomial orders is only available in the field file.

- Introduce new options for load balancing in the mesh partitioning, through the solver info `WEIGHTPARTITIONS`. Possible values are `DOF` (load balanced by number of degrees of freedom in each element), `BOUNDARY` (load balanced by number of boundary degrees of freedom in each element) or `BOTH`. By default, the current behaviour of using no weights is maintained. 


See merge request !617

Fix OCE third-party URL

This MR fixes the OCE third-party URL in the CMake configuration.

See merge request !681

# Conflicts:
#	CHANGELOG.md

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