Rename submit_form component to page_footer

Submit form was
- a confusing name in itself
- not descriptive, because it also has an optional ‘back’ link

This commit also puts this component in as many pages as possible, stripping
out any hard-coded buttons and links.

It replaces any usage of buttons for ‘back’, because these are links, not
buttons (ie they don’t change any data).

app/templates/views/edit-template.html

@@ -1,6 +1,6 @@
 {% extends "withnav_template.html" %}
 {% from "components/textbox.html" import textbox %}
-{% from "components/submit-form.html" import submit_form %}
+{% from "components/page-footer.html" import page_footer %}
 
 {% block page_title %}
 GOV.UK Notify | Edit template
@@ -13,9 +13,12 @@ GOV.UK Notify | Edit template
 		<form method="post">
 			{{ textbox(name='template_name', label='Template name', value=template_name) }}
 			{{ textbox(name='template_body', label='Message', small=False, value=template_body, highlight_tags=True) }}
-			{{ submit_form('Save and continue') }}
+			{{ page_footer(
+				'Save and continue',
+				back_link=url_for('.dashboard'),
+				back_link_text='Back to manage templates'
+			) }}
 		</form>
 
-  	<p><a href="manage-templates">Back to manage templates</a></p>
 
 {% endblock %}