Histogram tools branch + Contacts

Several modifications to the following modules:

• tools/helpers/histogramTools.py : fixed a bug on the findHistogramPeaks function.
• tools/label/label.py : added meanOrientation function.
• tools/label/contacts.py : added the following functions Spheroid, directionalErosion and, fixUndersegmentation.
• tools/label/contacts.py : fixed a bug on the contactOrientations function