LP#1422379 Move money.billing timestamps back to moment of fine

LP#1422379 Move money.billing timestamps back to moment of fine

Current code stamps billings into the future, with the underlying
concept that the time represents when the billing ends, not when it
begins.  This is hard to understand, and requires frequent explanation
to those not familiar with it.

Let's instead do the more natural thing and have the first billing come
one second after the due time, then every fine interval after that.

Signed-off-by: Dan Wells <dbw2@calvin.edu>