Use stringstreams in fitEffAcc.cc to buffer cout

Stringstream is used to buffer writes so that each part of the code only
calls cout once. This offers some protection against line mangling when
running fitEffAcc.exe via a multiprocessing configuration file.
Rename BackgroundLibrary.h to BinnedBackground.h

Also added in an analytic function for the background.
Parallelize fitEffAcc.cc Configure Scripts

run_eb_eb_and_eb_ee_fit.py and run_eb_hf_trigger_fit.py are now
parallelized using python's multiprocessing.

fitEffAcc.cc has had a few parameters tweaked for the fit and plotting
output.