URL-safe Base64 for use in routes and params

Two questions:
1) I used `Base64.urlsafe_encode64` instead because that seemed to make sense, that ok?
2) Should it locate with a base64 encoded signed gid? If so, I can add another commit for that.
Ah, it does look like `=` is the only unwanted char, and it is safe to remove if we manage the padding ourselves, as you do. Nice. I thought `?` and `&` were present as well, but it appears not. So we should be good to go with `urlsafe_encode64`!