Improvement to the handing of TH1s

 - Observation, Process and Systematic classes are now responsible for
   ensuring any TH1 passed in does not have negative bins, as well as
   performing the scaling to unit integral
 - The set_shape methods now take an extra bool which determines in the
   norm value should be updated to the histogram integral or not
 - New methods for getting clones or copies of the internal TH1 are
   added
 - basic implementation of flags to control the behaviour of
   CombineHarvester added. Currently plan to hard-code these to
   something sensible and add an interface later
trying to fix compile errors
add hzz4l test
add script for testing SM datacards
Merge pull request #11 from ajgilbert/andrew-dev

Improvement to the handling of TH1s