votes: fixup various minor issues.

* Add a gap between thumbnails on mobile.
* Adjust CSS for scores and vote buttons.
* Include "Private favorites" as an incentive on the user upgrade page.
* Fix vote buttons not being visible beneath thumbnails on mobile.
* Fix the "Show scores" link not preserving the current page number.
* Fix vote buttons being unintentionally enabled for all thumbnails by default.
* Fix banned and restricted users being able to favorite posts by
  tagging them with `fav:self`.
* Fix search engines being able to crawl /posts?view=score pages.
* Fix broken tests.

app/components/post_votes_tooltip_component/post_votes_tooltip_component.html.erb

@@ -1,6 +1,6 @@
 <div class="post-votes-tooltip thin-scrollbar">
-  <div class="text-center text-muted">
-    +<%= post.up_score %> / <%= post.down_score %> <%= upvote_ratio %>
+  <div class="text-center text-muted whitespace-nowrap">
+    +<%= post.up_score %> / -<%= post.down_score.abs %> <%= upvote_ratio %>
   </div>
 
   <div class="post-voters">