Configurable alert frequency/reminders

Since the level of available/remaining oil has varying levels of urgency, depending on the season, there should be some configurability around when or how often "low" alerts are sent.

For example, we should want to be reminded to order oil more frequently. Similarly, if the level is low in mid-May or mid-July, we probably don't need an alert about a low level. Or perhaps less frequent (weekly? triggered by watching the current price of heating oil for a "good deal"?)