Change post votes to work the same way as comment votes:
* Make the upvote arrow blue if you've upvoted the post, or grey if you
haven't. Likewise for the downvote arrow.
* Make it so you can click the upvote or downvote arrows to undo the vote.
* Don't show any notices when you vote on a post.
Also fix it so that votes work the same way on the posts page, the
comments page, and in the modqueue. Before it wasn't possible to undo
votes on the comments page or in the modqueue.
On the posts show page, in the favorites list, show favorites according
to the order they were added to the favorites table, rather than the
order they were added to the posts's fav_string.
On most posts these should be the same, but on old posts they may be
slightly different. The IDs of the first few hundred thousand favorites
don't appear to be in chronological order. Probably the original
favorite IDs were lost and recreated by a database move at some point in
Danbooru's history. The fav_string is also inconsistent with the
favorites table in some places (one contains favorites that aren't
contained by the other), which also throws off the order.
Partially addresses #4562 by eliminating one place where we depended on
the fav_string.
When favoriting/unfavoriting a post, it would also be upvoted/"un"voted
but the upvote/downvote/undo vote buttons would stay shown/hidden as
they were before unlike when pressing those buttons.
For example when you want change from favorite to merely upvoted you
would have to reload the page in between.
