emigration process on all population in one go
emigration(xp, perc.mig, emi.m, emi.table = NULL)
a list, first entry are updated pops, second entry the number of disperserin a matrix
all pops combined in a list
percentage if migrating individuals
emigration probability (normally based on cost dispersal distance)
a fixed number of migrating individuals can be specified (overrides emi.m)