Simple "ripe now" filter

[ezwelty]

A "ripe now" filter is the most oft-demanded feature by far. Although extremely complex to implement, we could start with the simplest possible version: filtering based on location.season_start and location.season_end, and possibly observation.fruiting_status (in conjunction with observation.observed_on).

A benefit of rolling this out early would be to give people added incentive to add this information to locations.

[ezwelty]

See discussion here: falling-fruit/falling-fruit#33