Add main_image_id column to listing
Set necessary instance variables for new and edit after validation failure
Add validation for presence true on listing image
Change up_to_four to check for length rather than count
Add instance methods to find main and marketplace images
Add extension white list, and marketplace version
Add tooltip on photos label, and radio button to set default picture
Add interchange to set image, add contional to not show price on listings with sale type offer
Add conditional to set placeholder pic if listing has no images