Make page titles consistent

This commit modifies the HTML `<title>` tags for all the pages. It makes two
main changes:
- make the title tag match the `<h1>` of the page, for better or worse
- put the service name after the page title, seperated by an en dash, as per
  GOV.UK

app/templates/views/text-not-received-2.html

@@ -1,7 +1,7 @@
 {% extends "withoutnav_template.html" %}
 
 {% block page_title %}
-GOV.UK Notify
+Check your mobile number – GOV.UK Notify
 {% endblock %}
 
 {% block maincolumn_content %}