Re-add menu to frontpage* that was missing from new layout.

Also integrate the login as administrator functionality in this menu.

modules/core/templates/_frontpage_menu.twig

+<div class="pure-g">
+  <div class="pure-u-2-3">
+    <div class="pure-menu pure-menu-horizontal">
+    <ul class="pure-menu-list">
+      <li class="pure-menu-item {% if frontpage_section == "welcome" %} pure-menu-selected{% endif %}">
+        <a href="frontpage_welcome.php" class="pure-menu-link">Welcome</a></li>
+      <li class="pure-menu-item {% if frontpage_section == "config" %} pure-menu-selected{% endif %}">
+        <a href="frontpage_config.php" class="pure-menu-link">Configuration</a></li>
+      <li class="pure-menu-item {% if frontpage_section == "auth" %} pure-menu-selected{% endif %}">
+        <a href="frontpage_auth.php" class="pure-menu-link">Authentication</a></li>
+      <li class="pure-menu-item {% if frontpage_section == "federation" %} pure-menu-selected{% endif %}">
+        <a href="frontpage_federation.php" class="pure-menu-link">Federation</a></li>
+    </ul>
+    </div>
+  </div>
+  <div class="pure-u-1-3">
+    {% if isadmin %}
+    <p class="float-r youareadmin">{{ '{core:frontpage:loggedin_as_admin}'|trans }}</p>
+    {% else %}
+    <p class="float-r youareadmin">
+        <a href="{{ loginurl }}">{{ '{core:frontpage:login_as_admin}'|trans }}</a>
+    </p>
+    {% endif %}
+  </div>
+</div>

modules/core/templates/frontpage_auth.twig

 {% set pagetitle = '{core:frontpage:page_title}'|trans %}
+{% set frontpage_section = 'auth' %}
 {% extends "base.twig" %}
 
 {% block content %}
-    {% if isadmin %}
-    <p class="right youareadmin">{{ '{core:frontpage:loggedin_as_admin}'|trans }}</p>
-    {% else %}
-    <p class="right youareadmin">
-        <a href="{{ loginurl }}">{{ '{core:frontpage:login_as_admin}'|trans }}</a>
-    </p>
-    {% endif %}
+    {% include "@core/_frontpage_menu.twig" %}
 
     <ul>
     {% for key, link in links_auth %}

modules/core/templates/frontpage_config.twig

 {% set pagetitle = '{core:frontpage:page_title}'|trans %}
+{% set frontpage_section = 'config' %}
 {% extends "base.twig" %}
 
 {% block content %}
-    {% if isadmin %}
-    <p class="float-r youareadmin">{{ '{core:frontpage:loggedin_as_admin}'|trans }}</p>
-    {% else %}
-    <p class="float-r youareadmin">
-        <a href="{{ loginurl }}">{{ '{core:frontpage:login_as_admin}'|trans }}</a>
-    </p>
-    {% endif %}
+    {% include "@core/_frontpage_menu.twig" %}
 
     <div style="margin-top: 1em;">
         <code style="background: white; background: #f5f5f5; border: 1px dotted #bbb; padding: 1em;  color: #555" >{{ directory }} ({{ version }})</code>

modules/core/templates/frontpage_federation.twig

 {% set pagetitle = '{core:frontpage:page_title}'|trans %}
+{% set frontpage_section = 'federation' %}
 {% extends "base.twig" %}
 
 {% block content %}
-    {% if isadmin %}
-    <p class="float-r youareadmin">{{ '{core:frontpage:loggedin_as_admin}'|trans }}</p>
-    {% else %}
-    <p class="float-r youareadmin">
-        <a href="{{ loginurl }}">{{ '{core:frontpage:login_as_admin}'|trans }}</a>
-    </p>
-    {% endif %}
+    {% include "@core/_frontpage_menu.twig" %}
 
     {% if metaentries.hosted is iterable and metaentries.hosted is not empty %}
     <dl>

modules/core/templates/frontpage_welcome.twig

 {% set pagetitle = '{core:frontpage:page_title}'|trans %}
+{% set frontpage_section = 'welcome' %}
 {% extends "base.twig" %}
 
 {% block content %}
-    {% if isadmin %}
-    <p class="float-r youareadmin">{{ '{core:frontpage:loggedin_as_admin}'|trans }}</p>
-    {% else %}
-    <p class="float-r youareadmin">
-        <a href="{{ loginurl }}">{{ '{core:frontpage:login_as_admin}'|trans }}</a>
-    </p>
-    {% endif %}
+    {% include "@core/_frontpage_menu.twig" %}
 
     <p>{{ '{core:frontpage:intro}'|trans|raw }}</p>
     <ul>