Rework pool versions index/diff views

- Changed to using the diff-body CSS class
-- Removed unneeded CSS style file
- Removed trailing whitespace after the >>> link
-- It was causing artifact line-throughs to appear after the link
- Changed the diff link to only render when a text field has changed
-- Because the post changes are already shown on the index view
- Specifically add <br> to statuses to cause line breaks

app/views/pool_versions/_diff.html.erb

@@ -11,7 +11,7 @@
   <% diff[:removed_post_ids].each do |post_id| %>
     <del>
       <%= link_to post_id, post_path(post_id) %><%#
-    %><%= link_to "»", pool_versions_path(search: { post_id: post_id }) %>
-    </del>
+    %><%= link_to "»", pool_versions_path(search: { post_id: post_id }) %><%#
+  %></del>
   <% end %>
 </span>