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

Parco 2019 debug

See merge request !930

Make the minimal SPH scheme collect the minimal time-bin of the neighbours in the force and use this when setting the time-step size.

Pass the hydro_properties to the prepare_gradient function. Make sure rho_dh is sensible when particles get ejected out of neighbourhoods.

Reported by @jborrow, closes #618.

Updated the IsolatedGalaxy_starformation python scripts to use the new snapshot names

See merge request !932

Alternative definition of the number of neighbours

See merge request !926

Add interactive task plot script.

See merge request !921