Use a bisection bracketing scheme around the Newton method in the ghost iteration to help with cases where we struggle and oscillate around the correct solution.

In the ghost smoothing length iterations check the convergence agains the initial value of h not against the previous one.

Added mechanism to add tracers information to the xparts. Added the EAGLE tracers (max(T) and time of max(T)). Tracers are dumped in snapshots.

Use the same naming convention for the hydro sort activation function and the star sort activation function.

Correctly update the counters when adding a spart to the global array. Handle the case where we run out of free slots.

Correctly link the newly created star to the ddestroyed gpart. Can survive time integration for a few steps. Crashes at next rebuild still.

Replace the absolute depth criterion for gravity tasks with a relative criterion based on the local depth of the tree.