add landmark roles to header and footer

wagtail/admin/templates/wagtailadmin/pages/create.html

@@ -7,7 +7,7 @@
 
 {% block content %}
 
-    <header class="merged tab-merged">
+    <header class="merged tab-merged" role="banner">
         {% explorer_breadcrumb parent_page include_self=1 %}
 
         <div class="row row-flush">
@@ -23,7 +23,7 @@
         <input type="hidden" name="next" value="{{ next }}">
         {{ edit_handler.render_form_content }}
 
-        <footer>
+        <footer role="contentinfo">
             <ul>
                 <li class="actions">
                     <div class="dropdown dropup dropdown-button match-width">

wagtail/admin/templates/wagtailadmin/pages/edit.html

@@ -34,7 +34,7 @@
             <input type="hidden" name="revision" value="{{ revision.id|unlocalize }}" />
         {% endif %}
 
-        <footer>
+        <footer role="contentinfo">
             <ul>
                 <li class="actions">
                     <div class="dropdown dropup dropdown-button match-width {% if is_revision %}warning{% endif %}">

wagtail/admin/templates/wagtailadmin/shared/header.html

@@ -17,7 +17,7 @@
     add_link - if present, display an 'add' button. This is a URL route name (taking no parameters) to be used as the link URL for the button
     add_text - text for the 'add' button
 {% endcomment %}
-<header class="{% if merged %}merged{% endif %} {% if tabbed %}tab-merged{% endif %} {% if search_form %}hasform{% endif %}">
+<header class="{% if merged %}merged{% endif %} {% if tabbed %}tab-merged{% endif %} {% if search_form %}hasform{% endif %}" role="banner">
     {% block breadcrumb %}{% endblock %}
     <div class="row nice-padding">
         <div class="left">