Implement leaf counting.

* timestream/manipulate/plantSegmenter.py (StatParamLeafCount): New class that
contains the statistical parameter for counting leaves.
(area, perimeter, roundness, compactness, eccentricity, mincircle): For all the
methods generating the statistical parameters add an img argument.
(StatParamCalculator.leafcount1): New method that calculates the number and
location of leaves within the pot. We applied  "3-D Histogram-Based Segmentation
and Leaf Detection for Rosette Plants" Jean-Michel Pape et. al. 2014.
* timestream/manipulate/pot.py (calcFeatures): Use new statistical parameter
calculator method with the new argument.