Rate-changing systematics

Since we didn't have the rate-changing systematics, added them in all scripts.
The values are in the cross section configuration:
```
rate_changing_systematics = {'luminosity': 0.026, #https://hypernews.cern.ch/HyperNews/CMS/get/physics-announcements/2526.html
                             'SingleTop_cross_section': 0.034, #https://twiki.cern.ch/twiki/bin/viewauth/CMS/StandardModelCrossSectionsat8TeV
                             'TTJet_cross_section': 0.043
}
```
The 7 TeV values were also changed accordingly (the single top cross section uncertainty was recommended to be 30% in 2011, apparently).

As expected, these systematics are very small (<0.05%).
The uncertainties due to lepton scale factors are shape-changing and need to be added separately.