IF: BLS key/signature encoding

[heifner]

Currently BLS public key and signatures are encoded as base64. This makes it difficult to copy/paste from terminals. Does this provide enough heart-ache to use a different encoding?

base64url would provide an easier to use format. We would want to change our base64url encoder not use the optional trailing = padding to make it easier to use. Specifically with --signature-provider which uses =KEY: as a separator.