using string-based secrets for easier debugging and help with issue v…

[jptmoore]

…alidating macaroons on ocaml with a binary-based secret

[yousefamar]

Could you turn on allow edits from maintainers real quick?

[yousefamar]

Summary of @jptmoore's changes: secrets are alphanumeric now instead of random bytes, and made longer to account for lost entropy. This is because of a currently unknown incompatibility between macaroons.js and ocaml-macaroons where one or the other encodes/decodes secrets differently (different charsets or so?) for the macaroon signing step, so this removes any ambiguity. @sevenEng, have you ever come across something like this before by any chance?

[jptmoore]

As discussed it might be worth removing the 2 step process of generating a secret then base64 encoding it to just generating something that can be transferred directly.