Issue by Novitsh: Refactor Scrambler fields to display a select in the admin interface instead of radios.

Issue #2751383 by Novitsh: File fields are removed from the selection on the administrative screen where you can initially add fields.

Issue #2751383 by Novitsh: On scrambling, detect if the field isn't a file, because files aren't supported in scrambling methods.

merging with x

merging