Simple Feature Request: Add Sort Collections by Number of Products

[RyanMalone]

Having the Collections section at the backend unable to sort by the number of products makes no sense.

It would be extremely useful, and very easy to implement to be able to sort by the number of products. It's a header already, you're able to sort by Title, so it makes no sense that this isn't an option. 

Being able to search for Tags etc. would be useful, but this is just a basic sort. 

Being able to check collections (when you have hundreds) that have zero or low numbers of items is just good practice and vital to any store. 

I can't believe that Shopify aren't already aware of this? It's far too basic, and we pay far too much for this to be another case of "there's an app for that".