Fixes to SimpleAnalysisFramework so the Sbottom2018 analysis can run

This MR changes a few bits so that the sbottom2018 analysis can run. These are mainly pertaining to soft-b-tagging.

Note - I really don't like the way the histogram needed is read in for every event, but for some strange reason, trying to put the histogram as a private member variable of the Soft-b-tagging class didn't work (it could setup the histogram in the init, but then whenever the values were retrieved from the Histogram in the event loop it'd segfault because the histogram had been removed from memory). If anyone has any better ideas for this I am very open to fixing it, but everything I tried failed.

I'm submitting this in the hope that the CI passes. Once we've agreed on these changes I will then merge the Sbottom2018.cxx to the other repo.

Cheers

John