Add admin template

ec-templates/admin.html

@@ -0,0 +1,17 @@
+<!-- htmlhint doctype-first:false -->
+{% extends "page.html" %}
+
+{% block main %}
+<div class="ecl-container ecl-u-mv-xl">
+  <div id="react-admin-hook">
+    <script id="jupyterhub-admin-config">
+      window.api_page_limit = parseInt("{{ api_page_limit|safe }}");
+      window.base_url = "{{ base_url|safe }}";
+    </script>
+    <script src="{{ static_url('js/admin-react.js') }}"></script>
+  </div>
+  <div class="container-fluid navbar-default small version_footer">
+    <div class="navbar-text">JupyterHub {{ server_version }}</div>
+  </div>
+</div>
+{% endblock %}