Better level for the time-step limiter task to make sure the gravity and hydro steps are synchronized.

Add the new global variable and some missing ones to the list of things written to and read from check-point files.

When doing a dry run that generates particles from the ICs, do not verify the (non-existing) particle links after creation of the gas particles.

SWIFT can not read DM background particles from the ICs using the particle type 2. These are treated as regular DM gparts after that.

This reverts merge request !839

Merge the changes from Jacob's particle leaving the box debugging branch that are unrelated to the fix itself.

Version that correctly flags the BHs to swallow and removes them before dying in the time-step calculation function.

Update the black_holes_struct.h file to contain a structure for the BHs and added functions to manipulate the structure.

Split the star formation task into two parts: The star formation bit and the resorting bit. Move the sf_count communication to just depend on the first one in order to speed things up.

Only call engine_rebuild() and not engine_init_particles() in main_fof. We don't need the full thing.