updated banners as per marketing's request

docsite/_themes/srtd/layout.html

@@ -198,10 +198,10 @@
 <!-- AnsibleFest and free eBook preview stuff -->
 <center>
 <a href="http://www.ansible.com/tower?utm_source=docs">
-<img src="http://www.ansible.com/hs-fs/hub/330046/file-2031636235-png/DL_Folder/festlondon-docs.png">
+<img src="http://www.ansible.com/hubfs/Docs_Ads/TowerDocs.png">
 </a>
-<a href="http://www.ansible.com/ansible-book">
+<a href="https://www.eventbrite.com/e/ansiblefest-nyc-2015-tickets-16058031003">
-<img src="http://www.ansible.com/hs-fs/hub/330046/file-2031636250-png/DL_Folder/Ebook-docs.png">
+<img src="http://www.ansible.com/hubfs/Docs_Ads/Untitled_design_1.png">
 </a>
 <br/>&nbsp;<br/>
 <br/>&nbsp;<br/>