Change allowance mechanics to always extend by `period` time.
Currently, when your contracts renew, they renew so that there is period
time left. This can create some confusing spending mechanics, where the first time you create contracts, you pay for 3 months of storage, but each time you renew after that you pay for 6 weeks of storage. It also means that up to your full allowance gets spent every 6 weeks, and users might be expecting that allowance to cover 3 months of storage, because indeed it does cover 3 months of storage for the first iteration only.
We can clear up a lot of this confusion just by making the allowance extend by the full period instead of extending up to the full period of time remaining.