User can add images, and user has easy-access to create new posts, admin can easily distinguish admin features

- Added admin divs on pages with features accessible only to admins, offset with css, for clarity.
- Added easy-access blocks for creating new ads on posts index and locations index pages.
- Added javascript to build url from dropdown in the location/index page easy-access block
- Added image url field to posts table
- Added image and post body divs in posts show page
- Added css to style new divs in post show page
@jsteiner @gabebw Can I avoid using a magic number for this? This tells the dropdown to select location #1, since I have no way of knowing what names will be available, it seemed likely that there will always be a first location, but this is ugly...