SDRF validator service and validated proof

[noatgnu]

This has been discussed and one of the suggestion for this service is a hosted SDRF validator service that anyone can use to validate their SDRF and it also provides something that would indicate either within the file itself using comment line ala #758 or another file that is the evidence or proof of a validation action performed by the service. This service maybe centrally hosted or there can be multiple hoster.

The simplest way for this is sha512 or sha256 with the content of the sdrf+ content of template + version of template + version of sdrf + version of validator. We can also include a unique signature to the hash to ensure that this has been generated from the specific service provider.

[ypriverol]

Great, idea, I think in issue #758 Im leaving a field in the metadata to make clear if the file has been validated or not.