Fix send-to-self for private messages, and add group query URLs

[peterbroadhurst]

I noticed that when I was only sending to myself, I was still getting data being pushed by FireFly core to DX.

Looks like when we made the identity change to introduce DIDs, we broke the code here:

firefly/internal/privatemessaging/privatemessaging.go

Lines 188 to 191 in 24d075b

	if node.Owner == localOrgDID {
	l.Debugf("Skipping send of %s for local node %s:%s for group=%s node=%s (%d/%d)", mType, ns, mID, group, node.ID, i+1, len(nodes))
	continue
	}

Also @hfuss mentioned to me that we've seen problems where the config has to have the full Key specification exactly as it gets resolved by the blockchain connector (so 0x prefix for ethereum, and the full CN=xyz... syntax for fabric), or things do not work correctly.

This PR:

• Ensures we always use the blockchain connector to get the resolved signing key
• Compares Owner of a Node to the signing key of the local org, not the DID
• Adds APIs to query groups, which seemed to be missing

[nguyer]

Looks good to me!