media assets: add thumbnail view to /media_assets page.

Add a thumbnail view to the /media_assets page. This page lets you see
all images uploaded to Danbooru by all users (although you can't see who
the uploader is). Also add a link to this page in the subnav bar on the
upload page.

app/views/iqdb_queries/show.html.erb

@@ -3,7 +3,7 @@
 
 <div id="c-iqdb-queries">
   <div id="a-check">
-    <h1>Similar Images Search</h1>
+    <h1>Reverse Images Search</h1>
     <section>
       <p>Paste a URL or upload a file to perform a reverse image search on <%= Danbooru.config.app_name %>.</p>
 
@@ -19,3 +19,5 @@
     <%= render "iqdb_queries/matches" %>
   </div>
 </div>
+
+<%= render "uploads/secondary_links" %>