Add standard back links to the support journey

Removes the non-standard, bottom of page back links where present.

Adds sticky footer to pages with long text boxes.

app/templates/views/support/report-problem.html

@@ -1,7 +1,8 @@
 {% extends "withoutnav_template.html" %}
 {% from "components/checkbox.html" import checkbox %}
 {% from "components/textbox.html" import textbox %}
-{% from "components/page-footer.html" import page_footer %}
+{% from "components/page-footer.html" import sticky_page_footer %}
+{% from "components/page-header.html" import page_header %}
 {% from "components/form.html" import form_wrapper %}
 
 {% block per_page_title %}
@@ -10,9 +11,10 @@
 
 {% block maincolumn_content %}
 
-    <h1 class="heading-large">
-      Report a problem
-    </h1>
+    {{ page_header(
+      'Report a problem',
+      back_link=url_for('.support')
+    ) }}
     <div class="grid-row">
       <div class="column-two-thirds">
         <div class="panel panel-border-wide">
@@ -29,11 +31,7 @@
             {% else %}
               <p>We’ll reply to {{ current_user.email_address }}</p>
             {% endif %}
-            {{ page_footer(
-              'Send',
-              secondary_link=url_for('.support'),
-              secondary_link_text='Back to support',
-            ) }}
+            {{ sticky_page_footer('Send') }}
         {% endcall %}
       </div>
     </div>