add duct-taped image fix

So, this is more of a duct-tape solution.

Basically - if the environment is "production" (Heroku) - assign images to each Item by setting the `photo_file_name`. And, since your images are in `public/assets/seed` -- I set the image to pull from there (`line 4` - _`item.html.erb`).

For non production enviro - the old way has to be as is.

As a side note - to increase seeding speed, I drastically adjusted the numbers for the seed data.

*This worked on my local, and http://dinner-dash-fo-rizzle-dizzle.herokuapp.com/ono-burrito*

Again, duct-taped --- but hopefully this won't hold you up from moving forward, and you can fix later if you have time!