Silly

Interesting to see what tasks complete first and last

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

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.

Added communication functions to propagate the new number of star particles after a SF event has occured.

Added basic support for black hole particles. Particles can be read in, attached to gpart, integrated forward in time, drifted and written to snapshots.

Added a force-communication with its dependency on the drift to make sure the data is correctly drifted before being received in the star loop.