WIP:Enable specific slices in menu tests
With this in place, every menu test (apart from RunMenuTest.py, which uses TriggerMenuMT) configures its slice directly from fullMenu.py
Eventually this should interact with a mechanism in TriggerMenuMT to enable only specific signatures and division of the menu by slice, as we had in Run 2.
WIP while I fix the references.
Cheers,
Stewart