ValidateDDOCommand - getValidationSignature only for authentificated requests

[alexcos20]

When calling ValidateDDOCommand we always add our signature if the DDO is valid, no matter who is the published. In order to implement the concept of isolated markets, we need to change that.

So, we will add our signature ONLY IF:

• command contains optional parameter publisherAddress
• command contains optional parameter nonce and nonce is valid for publisherAddress
• command contains optional parameter signature which is the signed message based on nonce by publisherAddress
• ddo.nftAddress exists and it's valid
• publisherAddress has updateMetadata role on ddo.nftAddress contract
• publisherAddress has publishing rights on this node (see DDO Index: Isolated node #815)