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_component/post_votes_component.scss

@@ -1,3 +1,5 @@
+@import "../../javascript/src/styles/base/000_vars.scss";
+
 .post-votes {
   // Fix it so that the vote buttons don't move when the score changes width.
   // XXX duplicated from app/components/comment_component/comment_component.scss
@@ -7,10 +9,11 @@
     min-width: 1.25em;
     white-space: nowrap;
     vertical-align: middle;
-
-    a {
-      color: var(--text-color);
-      &:hover { text-decoration: underline; }
-    }
+  }
+}
+
+.posts-container {
+  .post-score a {
+    @include inactive-link;
   }
 }