7_0_5_patch1 premix relvals update

-         process string set to differentiate 25ns/50ns pilep overlaid when done with premixed events (affects only wf injection to reqmgr)
-         --geometry Extended2015  as needs be in the 70x (all GT-driven in subsequent releases)
-         introduced SLHCUpgradeSimulations/Configuration/postLS1CustomsPreMixing wherever needed by premix workflows to adapt to Mike's #3973; ** TEMPORARY **