change key packet type accordingly in addSubkeyBindingCertificate
Revert "Expose PGPPublicKeyRing constructor"

This reverts commit 09d85b7d7a64b3003210d065c4210ff7fb7a8c6d, we can use
a workaround via streams to keep the api pure here.
Merge remote-tracking branch 'origin/spongy-master' into spongy-master