add slug field for use in obfuscating trip url
create slug when trip is saved
use slug to identify trips

The slug is used in the photo and trip controllers.
Posts in imgur upload, and editing JS have been changed to read the slug from the url.
The trip model returns the slug from to_param.
added .dup to url when fetching colors
copied missing images
photo variable assignment
Swtich to our fork of Miro to avoid frozen string errors on Heroku
update specs to use slug
Merge branch 'master' into obscure-trip-url
Merge pull request #51 from th7/obscure-trip-url

Obscure trip url