Support Stripping26 MC productions going to microDST

This is a general (not Turbo-specific) patch to support analysing microDST MC productions, and addresses LHCBGAUSS-1006.

It's mostly just back-porting some of @ibelyaev's nice microDST work, but also adds support for MC unpacking under RootInTES. This last addition will also need to make its way to master (the rest is already there).

I had to add PhysSel/PhysSelPython and Phys/AnalysisConf, so here's a prettier diff: 12afed8c...apearce-turbo-mdst-mc

@ibelyaev: there shouldn't be anything very controversial here (because you wrote most of it 😉) but I'd appreciate it if you had a look at my changes to AnalysisConf.unpackMC to check that things look sensible.