Fix issue with attempt to dump partition when not using MPI

Can also change the number of queues to match the threads (expected behaviour), the number of tasks per cell and the size of MPI messages, these all could be useful when re-starting

The lenghts are checked against the expected values and cause an error, the labels are not currently used (would need to add API to return the headers so that these could be speculatively queried and the stream rolled back, so maybe not a great idea).

Exits the application and writes restart files (regardless of other settings)

Sugar of various kinds, new parameters to control restart file dumping, better adherence to the restart_ name space, dumps on exit for testing restarts, include in step properties

Remove debugging output, tidy up output and make sure we return restart files in order, at least up to 1M files.

Make restart files dump after a number of hours from the start and synchronize dumps across MPI ranks

Needed to save and restore the current partition

Don't have any cells yet

Update the total number of particles in the run after the replication process.

See merge request !490

Moved restart_write into engine_step and trigger after drift_all

Tidies up the restart option

Unify the first initialisation of the part and xpart arrays. Correctly set the ti_drift and ti_kick for gparts and sparts.

Better function name for the first initialiation of all the parts at the very start of engine_init_particles()