Move logo images to images/logos directory

Author: yasulab

app/assets/images/case-shinjuku_logo.png renamed to app/assets/images/logos/case-shinjuku.png

@@ -115,13 +115,13 @@
     <h2>スポンサー</h2>
     <ul>
       <li><a href="https://case-shinjuku.com/">
-          <%= image_tag "case-shinjuku_logo.png"%></a></li>
-      <li><a href="http://www.osscafe.net/ja/">
-          <%= image_tag "osscafe_logo.png"%></a></li>
+          <%= image_tag "logos/case-shinjuku.png"%></a></li>
+      <li><a href="http://www.osscafe.net/">
+          <%= image_tag "logos/osscafe.png"%></a></li>
       <li><a href="https://scrivito.com/">
-	  <%= image_tag "scrivito_logo.png"%></a></li>
+	  <%= image_tag "logos/scrivito.png"%></a></li>
       <li><a href="https://yasslab.jp/">
-          <%= image_tag "yasslab_logo.png"%></a></li>
+          <%= image_tag "logos/yasslab.png"%></a></li>
     </ul>
   </section>
 </div>