Remove the REFILL_PERIOD, instead have the operator refills when reserves are low

[darosior]

The simulation currently is configured with a "refill period", whereas we expect stakeholders to be informed of low unallocated reserves on their WT to eventually refill it.

We should remove the REFILL_PERIOD to instead assumes that when the reserve goes low enough the operator will refill the WT, and track the refills (total number and block height).

What do you think @JSwambo ?