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.
Need tests here for `GlobalID.find(encoded_param)` (and `GlobalID.parse(encoded_param)` if you add that) :heart: