refactor share buttons

app/views/posts/partials/index/_share.html.erb

@@ -0,0 +1,19 @@
+<% if Danbooru.config.addthis_key %>
+
+<div class="addthis_toolbox addthis_default_style addthis_32x32_style">
+  <a class="addthis_button_twitter"></a>
+  <a class="addthis_button_facebook"></a>
+  <a class="addthis_button_reddit"></a>
+</div>
+
+<script type="text/javascript">
+  var addthis_config = {"data_track_addressbar": false, "pubid": "<%= Danbooru.config.addthis_key %>"};
+  var addthis_share = {
+    "url":"<%= j posts_url(tags: params[:tags]) %>",
+    "title": "<%= escape_javascript @post_set.humanized_tag_string %> - <%= Danbooru.config.app_name %>"
+  };
+</script>
+
+<script type="text/javascript" src="//s7.addthis.com/js/300/addthis_widget.js#async=1"></script>
+
+<% end %>