Move underscore templates out into separate files

cms/templates/js/chapter.underscore

+<li>
+  <div class="input-wrap">
+    <label for="chapter-<%= order %>-name"><%= gettext("Chapter Name") %></label>
+    <input id="chapter-<%= order %>-name" name="chapter-<%= order %>-name" placeholder="<%= _.str.sprintf(gettext("Chapter %s"), order) %>" value="<%= name %>">
+    <p class="help_text"><%= gettext("the title/name of the chapter that will be used in navigating") %></p>
+  </div>
+  <div class="input-wrap">
+    <label for="chapter-<%= order %>-asset-path"><%= gettext("Chapter Asset") %>:</label>
+    <input id="chapter-<%= order %>-asset-path" name="chapter-<%= order %>-asset-path" placeholder="<%= _.str.sprintf(gettext("path/to/introductionToCookieBaking-CH%d.pdf"), order) %>" value="<%= asset_path %>">
+    <p class="help_text"><%= gettext("provide the path for a file or asset already added to this course") %></p>
+  </div>
+  <input type="button" value="<%= gettext("Upload Asset") %>">
+  <a class="action-close">close-button</a>
+</li>

cms/templates/js/textbook.underscore

+<form>
+  <div class='input-wrap'>
+    <label for="textbook-name-input"><%= gettext("Name") %>:</label>
+    <input id="textbook-name-input" type="text" placeholder="<%= gettext("Introduction to Cookie Baking") %> value="<%= name %>">
+    <p class="help_text"><%= gettext("the title/name of the text book as you would like your students to see it.") %></span>
+  </div>
+  <ol class="chapters"></ol>
+  <p><%= gettext("Note: <strong>It's best practice to break your course's textbook into multiple chapters</strong> to reduce loading times for students. Breaking up textbooks into chapters can also help with students more easily finding a concept or topic-based information.") %></p>
+  <button class="add-chapter"><%= gettext("Add a Chapter") %></button>
+  <div class="buttons">
+    <input type="submit" class="action-primary" value="<%= gettext("Save") %>" />
+    <input type="button" class="action-secondary action-cancel" value="<%= gettext("Cancel") %>" />
+  </div>
+</form>

cms/templates/textbooks.html

 <%inherit file="base.html" />
+<%namespace name='static' file='static_content.html'/>
 
 <%block name="title">Textbooks</%block>
 <%block name="bodyclass">is-signedin course textbooks</%block>
 
 <%block name="header_extras">
-<%text>
   <script type="text/template" id="new-textbook-tpl">
-    <form>
-      <div class='input-wrap'>
-        <label for="textbook-name-input"><%= gettext("Name") %>:</label>
-        <input id="textbook-name-input" type="text" placeholder="<%= gettext("Introduction to Cookie Baking") %> value="<%= name %>">
-        <p class="help_text"><%= gettext("the title/name of the text book as you would like your students to see it.") %></span>
-      </div>
-      <ol class="chapters"></ol>
-      <p><%= gettext("Note: <strong>It's best practice to break your course's textbook into multiple chapters</strong> to reduce loading times for students. Breaking up textbooks into chapters can also help with students more easily finding a concept or topic-based information.") %></p>
-      <button class="add-chapter"><%= gettext("Add a Chapter") %></button>
-      <div class="buttons">
-        <input type="submit" class="action-primary" value="<%= gettext("Save") %>" />
-        <input type="button" class="action-secondary action-cancel" value="<%= gettext("Cancel") %>" />
-      </div>
-    </form>
+    <%static:include path="js/textbook.underscore" />
   </script>
-
   <script type="text/template" id="new-chapter-tpl">
-    <li>
-      <div class="input-wrap">
-        <label for="chapter-<%= order %>-name"><%= gettext("Chapter Name") %></label>
-        <input id="chapter-<%= order %>-name" name="chapter-<%= order %>-name" placeholder="<%= _.str.sprintf(gettext("Chapter %s"), order) %>" value="<%= name %>">
-        <p class="help_text"><%= gettext("the title/name of the chapter that will be used in navigating") %></p>
-      </div>
-      <div class="input-wrap">
-        <label for="chapter-<%= order %>-asset-path"><%= gettext("Chapter Asset") %>:</label>
-        <input id="chapter-<%= order %>-asset-path" name="chapter-<%= order %>-asset-path" placeholder="<%= _.str.sprintf(gettext("path/to/introductionToCookieBaking-CH%d.pdf"), order) %>" value="<%= asset_path %>">
-        <p class="help_text"><%= gettext("provide the path for a file or asset already added to this course") %></p>
-      </div>
-      <input type="button" value="<%= gettext("Upload Asset") %>">
-      <a class="action-close">close-button</a>
-    </li>
+    <%static:include path="js/chapter.underscore" />
   </script>
-</%text>
 </%block>
 
 <%block name="jsextra">