composition from  tuplecleanup, working version
implement rightLegend
bugfix cache, right legend
go back to the loose mu (tag) + el(probe) samesign region for sf

This is the selection I needed to test for the electron scale factor
when replacing the bbbar sample with
filelist/Pythia8B_AU2_CTEQ6L1_bbTomu15.txt
Processes with
```
measureFakeRate \
 -i filelist/Pythia8B_AU2_CTEQ6L1_bbTomu15.txt \
 -o trashbin/test_bb_normalization/Pythia8B_AU2_CTEQ6L1_bbTomu15_Apr_20.root \
 -s Pythia8B_AU2_CTEQ6L1_bbTomu20 \
 --write-tuple
```

then made a bunch of tricks to replace the bbar tuple (see worklog
2014-05-01 for details). The new sample is not helping, will need to
apply a pt_mu>20 to avoid the trigger bias.
dummy commit, just for reference on bb15 sample
compositions: just split by channel, no kin req
el_scale_factor: restore bb20 norm factor, apply pt_tag>20
buildWeightedMatrix: move funcs to fakeUtils
compute_fake_el_scale_factor fix cache (typo)
compute_eff_from_ntuple: initial version, working