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.
Factor out FontAwesome icons into a set of helpers. This is so that it's
easier to keep track of which icons we're using and easier to change
icons globally.
Side effects:
* The data-current-user-is-voter <body> attribute has been removed.
* {{upvote:self}} no longer works. {{upvote:<name>}} should be used instead.
Refactor tag_list_html, split_tag_list_html, and inline_tag_list_html to
take the `show_extra_links` and `current_query` options explicitly,
rather than implicitly relying on CurrentUser or taking `params[:tags]`
from the template.
