posts: rework post events page.

* Add a global /post_events page that shows the history of all approvals,
  disapprovals, flags, appeals, and replacements on a single page.

* Redesign the /posts/:id/events page to show all approval, disapproval,
  flag, appeal, and replacement events for a single post (before it only
  showed approvals, flags, and appeals).

* Remove the replacement history link from the post show page. Replacements
  are now included in the post events page (closes #4948: Highlighed replacements).

* Add /post_approvals/:id and /post_replacements/:id routes (these are
  used by the "Details" link on the post events page).

app/views/static/site_map.html.erb

@@ -18,9 +18,10 @@
       <ul>
         <li><h2>Post Events</h2></li>
         <li><%= link_to("Tag History", post_versions_path) %></li>
+        <li><%= link_to("Events", post_events_path) %></li>
+        <li><%= link_to("Appeals", post_appeals_path) %></li>
         <li><%= link_to("Approvals", post_approvals_path) %></li>
         <li><%= link_to("Disapprovals", post_disapprovals_path) %></li>
-        <li><%= link_to("Appeals", post_appeals_path) %></li>
         <li><%= link_to("Flags", post_flags_path) %></li>
         <li><%= link_to("Replacements", post_replacements_path) %></li>
       </ul>