Refs #10200.  Added property MinimumPeakHeightObs.

To FindPeaks, GetDetOffsetsMultiPeak and CalibrateRectangularDetectors.
On branch feature/10200_findpeaks_min_maxobsy
Changes to be committed:

      modified:   ../Mantid/Framework/Algorithms/inc/MantidAlgorithms/FindPeaks.h
      modified:   ../Mantid/Framework/Algorithms/inc/MantidAlgorithms/GetDetOffsetsMultiPeaks.h
      modified:   ../Mantid/Framework/Algorithms/src/FindPeaks.cpp
      modified:   ../Mantid/Framework/Algorithms/src/GetDetOffsetsMultiPeaks.cpp
      modified:   ../Mantid/Framework/PythonInterface/plugins/algorithms/CalibrateRectangularDetectors.py
Merge branch 'feature/10200_findpeaks_min_maxobsy' into develop