merchant can edit products

@cgruppioni @aslawter 

This branch was repurposed after it was created to focusing on editing as a whole. The branch name was changed locally, but I haven't been able to do anything about the name here.
This was just the first thing that occurred to me that worked. I don't know which one is better, but I kind of like this  because it gets rid of a line. Let's see what Gabe/Steiner have to say about it.