Create growingrecs.py

Command-line tool to find the most common planting conditions for a given crop. This version counts combinations of planted_from and sunniness, but as planted_from is often left blank this may not be the best choice.
I don't think we necessarily need to combine these.  We can just roughly replicate what's in the sidebar of the crop page, eg:

Plant from: seed (18), seedling (4)
Plant in: sun (22), semi-shade (10) 

You could express this as a percentage if you liked.  But I'm thinking that the combined version is a) quite a lot of complicated code, and b) not actually as useful as it might seem -- as a gardener, I don't actually need that combined information.  If we want this to be the simplest possible API example, we don't need to do all that.