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.
Originally I changed the locator test id to ensure the equals signs went through, but since I added the decoding to parse I added some tests in this file.