Scradd Chat: Handle links better

[cobaltt7]

Any response containing non-Discord links should be ignored, otherwise, they could be used for advertisement.

Discord links and channel mentions should be converted to a mention of a random public channel in SA. If the original is a link to a message, the output should scroll to a random place in the channel. This can be done by selecting a random date between now and the channel's creation and converting it to an empty snowflake.