Add item_images table and associations
Add associations for Item/ItemImages
Create nested images resource; fix typos
Update paperclip stuffs in ItemImage
Add test for item_image
Add first pass at test for multiple items
Remove image from item; stub out tests for now
Fix merge conflicts
Remove duplicate price validation on Item
Update seed data to no longer create images for items

This is based on the fact that we now have multiple images per item,
meaning that the seed data will be updated using ItemImages.
Change title of items#edit to 'Update your Listing'
ItemImages now saved through items#edit form

Update listing now redirects to the individual item path.
Add controller for item images
Add two-part form
Fix merge conflicts
Merge pull request #127 from MarcGarreau/images

Images