Wrap splits functions - for ParMmg convenience

[laetitia-m]

1. Wrap the splits functions used in LS mode (split1, split2sf, split3cone and split4op) for ParMmg convenience. In the splits, the configuration is determined based on the vertices indices. In ParMmg, we need to use the global vertices numbering instead of the local (in term of proc) vertices numbering: to allow this, split functions have been modified to be able to specify the tetra vertices numbering as argument. This change has no impact on mmg.
2. Rename some split configuration functions for consistency (e.g. MMG3D_configSplit3op becomes MMG3D_split3op_cfg).

[Algiane]

Thanks