Correctly include the velociraptor particle information in the Makefile. Re-arrange the content of the inteface files slightly.

Swift velociraptor

See merge request !578

Drift all particles before a repartition event. Update the debugging check to verify that everything is drifted to the correct time.

Make the STF dump follow the same pattern as the other dumps. A drift_all will have to be added one day.

Call the gpart functions rather than reading directly their fields in the velociraptor interface. Temporary workaround for stars.

Lean gravity option

See merge request !579

Do not duplicate lines in the timestep file when restarting. Also print the redshift and not just the scale-factor.

Drift the particles to the current time before rebuilding when restarting a run from a check-point file.

Conflicts:
	src/engine.c

Gravity splittask (non-MPI)

See merge request !576