Implement premium payments-per-year handling other than through alpha/beta
Some tariffs handle premium payment frequencies >1 not with the alpha(m) and beta(m) factors, but rather through different cost factors applied to yearly payments.
The difference to the alpha(m)/beta(m) handling with order 0 is that the PV formula contains the additional term 1/m! Somehow we need to get rid of this in a well-structured, non-hackish way.