Grackle chemistry --> GEAR chemistry. Moved the output of subgrid model to a separate part of the HDF5 file.

Correct wrapping of particles

See merge request !489

Better naming convention for the cell_split variables in the YAML file. New variable for the splitting of gravity pairs.

This reverts commit 10f04895.

When two particles are at the same position in ICs give more information about the particles involved.

Added a branching function for DOSELF_SUBSET. To call vectorised version when…

See merge request !488