Added "cal_generation" and "get_generation" 

The function "editPed" adds missing individuals to the pedigree and orders it according to generations.
It is nicely implemented in plain R, but unfortunately painfully slow on large pedigrees.
I added two functions that calculate the generation for every individual of the pedigree.
Those functions and the being called from the R-function "editPed". So the behaviour and syntax
on the R-level are preserved