Easy upvoting by duplication

[christhompson]

Currently, loredb will warn when it detects a duplicate lore attempt (and exit).

Now that loredb has upvote/downvote support, duplicate loredb add should instead be treated as upvotes. This is a simple change to add some upvote support via lorebot, without a more involved integration (separate upvote/downvote reaction integration).

This should be able to directly reuse the duplicate lore detection code.