Fix JS dependency issues

textbook.js is apparently being loaded on every page, so I just made sure that
Backbone Associations was also loaded on every page to be sure that the dependency
was always being met.

cms/templates/base.html

@@ -40,6 +40,7 @@
     <script type="text/javascript" src="${static.url('js/vendor/underscore-min.js')}"></script>
     <script type="text/javascript" src="${static.url('js/vendor/underscore.string.min.js')}"></script>
     <script type="text/javascript" src="${static.url('js/vendor/backbone-min.js')}"></script>
+    <script type="text/javascript" src="${static.url('js/vendor/backbone-associations-min.js')}"></script>
     <script type="text/javascript" src="${static.url('js/vendor/markitup/jquery.markitup.js')}"></script>
     <script type="text/javascript" src="${static.url('js/vendor/markitup/sets/wiki/set.js')}"></script>
 

cms/templates/textbooks.html

@@ -25,9 +25,6 @@
 </%block>
 
 <%block name="jsextra">
-<script type="text/javascript" src="${static.url('js/vendor/backbone-associations-min.js')}"></script>
-<script type="text/javascript" src="${static.url('js/models/textbook.js')}"></script>
-<script type="text/javascript" src="${static.url('js/views/textbook.js')}"></script>
 <script type="text/javascript">
 window.UPLOAD_ASSET_CALLBACK_URL = "${upload_asset_callback_url}"
 window.TEXTBOOK_URL = "${textbook_url}"