Change Sim10 slot to based it on LCG_100
Change reference Sim10 slot to prepare release based on LCG_100.
As a result, put explicit dependencies on gauss-conf and align gauss-dev.
Also put back LHCB_5 layer for lhcb-gen for powheg as otherwise plenty of (fake) errors reported.
Will need to see how to apply new rivet in lhcb-gen2 since need new madgraph version from LHCB_6.