Added function to count number of taxa with inferred losses for each db.
Added function to count number of taxa with inferred losses for each db.

New function is count_lossTaxa in infer_age. The count is found by subtracting
the number of taxa with orthologs from the total number of taxa descending
from the ancestral node in the tree. Note that this is not the same as number
of loss events.

bliebeskind/Gene-Ages