Tidies up the restart option

Start reorganizing so we can restart, doesn't work yet

Make use of a temporary threadpool in the reading routines to speed-up the duplication of parts into gparts.

Open only once dependency file and add an option in debugging-checks mode for writing task dependency graph

Add information to stdout and timestep.txt about what happened in the step (rebuild, repartition, snapshot, ...)

When compiling with the iosthermal equation of state, read the constant thermal energy from the YAML file.

There is a problem when the cpu mask is empty and using multiple MPI ranks on a node, in that case all the main threads end up pinned to one core during the reading of the initial condition (and any other tasks done before engine_init is called).

Compute one octant of the Ewald corrections at start-up for future use when running with the gravity checks.

This reverts merge request !375

Make sure the GIZMO extra loop uses the in and out ghost tasks and not just the main ghost task. Code formatting.

This is a requirement of fopen()