Replace beam histogramming implementation for 1D.  Add beam min value.

* beam keeps the original pixel array, stores the histogrammed
  one in an additional array.  This changes the interface to the
  histogrammed beam, so the model files, etc. had to be changed.
* nbins is now a parameter instead of histlogstep.  Changes specFile.
* Support minimum accepted beam value.  This can be important when
  histogramming, or one gets rather poor sampling.  Default is 1e-5.
* Unit tests pass (some had to be updated).