ellisztamas/faps: Human-readable summary of paternity of individual progeny

Added function to return human readable results about the top candidate fathers for each individual offspring in the data set. This essentially a summary function for sibshipCluster.posterior_paternity_matrix().

• Added method paternity to sibshipCluster objects to return a table for that halfsib array only giving the IDs of the mother, offspring, and the N candidate fathers with the highest posterior paternity, along with those probabilities.
• To do this I needed to update sibshipCluster to inherit offspring names from paternityArray objects.
• Renamed sibshipCluster.prob_paternity to the more intuitive posterior_paternity_matrix