Add support for creating and verifying BBS+ credentials

[TimoGlastra]

Context

Spec: https://w3c-ccg.github.io/ldp-bbs2020/
Library: https://github.com/mattrglobal/jsonld-signatures-bbs

Todo

• Research what library we should use for BBS+ in react native
  • Native Java & Obj c wrappers OR asm.js
  • If askar already supports BBS+ to sign, we need another solution for Node.JS
  • how easily can we switch from the easier asm.js to obj-c and java later on
  • contact Mattr on how they are using the native wrappers / bbs libraries in react native