Updates for CombineTools

CombineHarvester updates:
  * An extra ParseDatacard function that can extract the mass, analysis,
  channel, era and bin_id fields from the filename. Requires a
  user-specfied regex-style string.
  * A ForEach function for Observation, Process and Nuisance. User
  supplies the function.
  * A new helper function: OpenFromTFile. Will be rolled out across the
  framework at some point. Extracts objects from root files using the syntax
  "/path/to/file.root:path/to/some/object"
  * A new helper function: SetStandardBinName. A template function
  that will take an Observation, Process or Nuisance and set the
  bin field to analysis_channel_binid_era. Needed for H->tt where
  the same bin names are used for 7 TeV and 8 TeV (creating
  headaches)
  * New program, NuisanceSummary that will print a nicely-formatted
  digest of systematics in the chosen datacards
adapt PostFitPlot2 to use the CombineHarvester