Include Marriage ATXs in full in Checkpoint restore

[fasmat]

Description

We need to ensure that Marriage ATXs are included with their blobs in a checkpoint. The reason is that several malfeasance proofs (e.g. Invalid Post, Double Merge, etc.) require the original blob to be able to proof that different identities were actually merged.

Implementation hints

Alternatively a checkpoint could include just the proofs of marriage instead of the full ATX. This would require:

• The signatures in the Marriage Certificates
  • Additionally information about which nodeID created which signature (currently only available indirectly via the ReferenceAtx)
• The merkle (sub-)tree that proofs that those certificates were included in the marriage ATX, as well as the signature for that ATX and the identity that created that signature/ATX