[PR-584] IRCv3 Labeled Response

[justjanne]

In Short

• Unify codepaths for generating messages (partially done)
• Cleanup codepaths for handling IRC messages
• Create new Quassel feature for clients supporting message updates
• Create new database field for messages storing whether they’ve been received by the IRCd
• Attach a UUID to every sent message
• Upon receiving a message from the IRCd in response to a sent message, replace the sent message with the IRCd’s version
• Allow clients to attach a UUID to sent messages, use the same UUID for sending messages to IRC servers
• Update the UI to distinguish between three different UI states: In transit to core, In transit to IRCd, delivered