Show nearby plantings/harvests in planting reminder email

[Skud]

The planting reminder email should show what people near you are planting/harvesting, to give you inspiration.

We should write this as a reusable method, so we can potentially show the information on the website too (though we haven't currently got a clear idea of where on the website that would be... perhaps on the redesigned signed-in homepage

[Skud]

Something to consider: we don't want to use a fixed distance or timescale. What is relevant will vary depending on context. For instance if I have many local members, it might be useful to tell me what people within a 10km radius are planting this week. However if I don't have many local members or my local members aren't active, we might need to span out to 100km and 1 month to get a list of recent plantings.

[oshiho3]

I'm going to do this as well as #720.

[oshiho3]

harvest model doesn't have association to garden, so We'll be using owner's location. For planting, both owner and garden are available. Which one do we want to pick as location?

[oshiho3]

I was working on this one but have since dragged away due to lack of time. I've decided to drop this item as well as #720, so feel free to take it and work on this.