[SMHTT2017-dev] Added uncertainty model for embedded events

[janekbechtel]

Changes:

• Contains the two commits of Stefan's @stwunsch PR https://github.com/cms-analysis/CombineHarvester/pull/169 (so this one could be pulled and the other closed)
• Updated background process selection depending on the "embedding" or "jetfakes" switch
• Included two processes "EMB" = mu->tau embedded events and "TTL" = ttbar-> prompt lepton+tau. This is needed since ttbar->tau tau are included in embedded events, and only ttbar-> prompt lepton+tau need to be determined by MC (so TTL is a subset of TTT)
• Included uncertainties for embedded events (hadronic tau track efficiency, ttbar contamination, normalization)