adds new attributes to listings

uses paperclip gem, new locations include main image, and compiled address.
the compiled address will be used by the geocoder gem set that I have in another branch
:) Here's my thinking: to use the geocoder gem (i have it in another branch), I need a column with the full address (?). So I can have users enter in info for individual columns ("city", "street", "number"), then in the model I can create a new concatenated address. that new address gets saved in another column "full_address" and used by the geocoder.