Rename "TOS" efficiencies to "TrueSim" efficiencies in HltEfficiencyChecker to avoid confusion
Closes #23 (closed)
As discussed in #23 (closed), a few people are getting confused by the TOS efficiencies in HltEfficiencyChecker, thinking that it is the same TOS as Run 2 etc. so here I rename it throughout to TrueSim efficiencies as agreed in that issue discussion. The documentation is also changed in Moore!1298 (merged).
I also take this opportunity to do some modernization and cleaning up of HltEfficiencyChecker/scripts/hlt_line_efficiencies.py.
All tests pass locally for me so this ready for testing. Goes with Moore!1298 (merged).