Merge branch 'sink_star_formation' into 'master'

...es/IsolatedGalaxy/IsolatedGalaxy_sink/isolated_galaxy.yml

examples/IsolatedGalaxy/IsolatedGalaxy_sink/run.sh

examples/main.c

src/cell.h

src/cell_convert_part.c

src/cell_hydro.h

src/cell_split.c

src/cell_unskip.c

src/engine.c

src/engine_maketasks.c

src/engine_marktasks.c

src/engine_unskip.c

src/runner.h

src/runner_main.c

src/runner_others.c

src/runner_time_integration.c

src/scheduler.c

src/sink/Default/sink.h

src/sink/Default/sink_part.h

src/sink/GEAR/sink.h