This commit modifies the SignAnnouncement helper function to instead
take a MessageSigner interface rather than the deprecated MessageSigner
struct. We also modify the function to explicitly take the identity
public key to use when signing.
This commit implements some minor coding style, commenting and naming
clean up after the recent major discovery service was merged into the
codebase.
Highlights of the naming changes:
* fundingManager.SendToDiscovery -> SendAnnouncement
* discovery.Discovery -> discovery.AuthenticatedGossiper
The rest of the changes consist primary of grammar fixes and proper
column wrapping.
