Number of products

@czue @esoergel @twymer @nickpell 

This graph was dependent on archive-products being merged. 

Adds created_at and last_modified timestamps to products.
Actually I just looked back at this. This will need to have a reference to both SQL and couch objects, so it's basically iterate in couch look up in SQL or vice versa.

I think the best optimization may be to keep the loop as it is now and move line 15 and 16 into the if block so it's only looked up if modified.

Thoughts?