First public version of lepton SFs script

Currently the script performs tag and probe studies using the following BLT ntuples:
```
/hdfs/TopQuarkGroup/trigger_BLT_ntuples/Single*2011_RunAB_trigger_study.root
```
which were produced&merged using [these](https://github.com/BristolTopGroup/NTupleProduction/tree/master/Configuration/trigger_studies) configurations.

- So far only for 2011 7 TeV, hence no need for MC studies (just data)
- The script produces various plots, most importantly the efficiency plots in pt (turn ons) and eta
- Not yet factorised the ele+jets trigger efficiency, only electron leg is measured
- Not yet categorised in trigger objects (as shown [here](https://github.com/BristolTopGroup/NTupleProduction/blob/master/python/BristolNTuple_TriggerObjects_cfi.py), with supplementary summaries for [2011](https://gist.github.com/senkin/744807f9c12139231952) and [2012](https://gist.github.com/senkin/4249611cfab89e7fbc2f)). Currently using just [this](https://github.com/BristolTopGroup/NTupleProduction/blob/master/python/BristolNTuple_TriggerObjects_cfi.py#L15) electron leg of the e+jets cross trigger and [this](https://github.com/BristolTopGroup/NTupleProduction/blob/master/python/BristolNTuple_TriggerObjects_cfi.py#L58) single muon trigger.
- Not yet binned in pt and eta
- The selection applied to probes is currently only isolation and ID. Possibly need to apply impact parameter and conversion rejection cuts as per [this](https://twiki.cern.ch/twiki/bin/viewauth/CMS/KoPFAElectronTagAndProbe) twiki