Few fixes/tweaks for the Cache app, but still a bit to go

Hey man,

Here are a few things I did to tweak the application. There's actually a few more things to do to make it more secure, but I figured I had already changed a lot of things already :)
But we should actually make this a token instead of using the cover_photo_id, because someone could easily increment the cover_photo_id to see other photos or attach a different cover_photo to their listing.