Supercells Overlay implementation
checks for the presence of background events driven by Key and merges then into LArDigits for SuperCells. Part of the Overlay for the L1Calo. Initial configuration performed here. Given that I am not sure about all the tests I must perform, I will create this MR not as a draft. I already tested the Overlay part itself (technically, more checks needed) with a command from @jchapman.
Edited by Denis Oliveira Damazio