Function verifyProofGraphs

Check a series of proof graphs, ie, check whether the included signature of a proof graph corresponds to the hash value.

The following checks are also made for each proof graph:

1. There should be exactly one proof value
2. There should be exactly one verification method, which should be a separate resource containing the key (in JWK)
3. The key's (optional) expiration and revocation dates are checked and compared to the current time which should be "before"
4. The proof's creation date must be before the current time
5. The proof purpose(s) must be set, and the values are either authentication or verification

Errors are stored in the report structure. If any error occurs in any proof graph the result is false; otherwise, result is the conjunction of each individual proof graph verifications.