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.
Merge branch 'heroku-master' into obscure-trip-url-wip
update specs to use slug
only display user's own trips
no all users or all trips options
redirect to all trips or new trip from main#index when logged in
Merge remote-tracking branch 'origin/master' into only-own-trips

Kept changes, removed unused section, updated beta message

Conflicts:
	app/views/main/index.html.erb
Merge remote-tracking branch 'origin' into only-own-trips

Conflicts:
	app/models/trip.rb
	spec/controllers/trips_controller_spec.rb
Merge pull request #52 from th7/only-own-trips

Only own trips (Y)