use requestor as message link author instead of linked message author

[danthe1st]

When sending a message link, the bot automatically responds a copy of the linked message. The delete button currently allows the author of the original message as well as moderators to delete that copy.

This PR changes that behavior to allow the author of the message link (to which the bot responds to) to delete the message instead of the author of the original message.

Alternatively, it would be possible to configure both the original author and the requestor to delete the message.