Linking plain messages, resolves #2876.

[Jerrie-Aries]

Resolves linking plain messages, issue #2876.

Linking messages here is still using the old logics with some improvements:

• Use yarl library to store and retrieve data in embed's author url.
• Return early when reacting on non-thread message in DM's. No more Failed to find linked message for reactions error flooding the console.
• Use basic regex to retrieve mod tag/name when editing plain message. Alternatively if it fails (most likely not going to happen), the tag will be recreated from the mod that executes the command.

Current limitations:

• Reactions from user on their own messages will only be transfered to thread channel (not to other recipients).
• Reactions from other recipients will be ignored.
• Reactions on other recipient's messages in DM's will only be transfered to the owner of the message.

New thread data stored in author URL:

• type: The thread message type, e.g thread_message, note, persistent_note.
• from: Whether the original message was from mod or recipient.
• anonymous: The message was replied anonymously.
• plain: The message was replied in plain.

Psst: This is my 4th attempt creating a PR for this issue. Hopefully this will solve it.