Merge branch 'new_cosmo_ICs' into 'master'
New cosmo ICs New ICs to replace the BigCosmoVolume at some point. They contain corrected smoothing lengths such that the initialisation step is much shorter. They also contain the DM particles and further species for when we are ready to have them in SWIFT. The EAGLE_25 case is almost the old BigCosmoVolume. See merge request !188