Centrality tuple tool update
I have expanded the usage of the centrality tuple tool to also consider the PbNe collision system. For these I moved the assignment of some variables from the header to the initialise function, because now the values depend on the collision system set by the user ("PbPb" or "PbNe", case insensitive). If the collision system does not match either "PbPb" or "PbNe", the tool returns a fatal error. The procedure to get the numbers for "PbNe" is the same as the one used for "PbPb" detailed in the note LHCb-INT-2020-013, and is in the process of being documented in more detail in an analysis note aiming to be a DP paper.