Fix a division by zero when calculating the upvote ratio in the votes tooltip.
This could happen if the post had votes according to the post_votes
table, but didn't have any votes according to the up_score and
down_score. This should never happen, yet it did happen for post 2248039
and post 2959269.
Allow admins to remove votes on posts. This is for fixing vote abuse.
Votes can be removed by going to the vote list on the /post_votes page,
or by clicking on a post's score, then using the "Remove" option in the
"..." dropdown menu next to the vote.
Votes are soft-deleted - they're marked as deleted in the database, but
not fully deleted. Removed votes are only visible to admins, not to
regular users. When a vote is removed by an admin, it leaves a mod
action.
Technically it's possible to undelete votes, but there's no UI for it.
