Make nav and page headings reflect permissions

> If you have the Edit templates permission but not the Send messages permission, the navigation should read
>
> - Text message templates
> - Email templates
> - Letter templates
>
> The page headings should also read
>
> - Text message templates
> - Email templates
> - Letter templates

respectively

https://www.pivotaltracker.com/story/show/115488955

app/main/views/send.py

@@ -37,8 +37,8 @@ send_messages_page_headings = {
 
 
 manage_templates_page_headings = {
-    'email': 'Manage templates',
-    'sms': 'Manage templates'
+    'email': 'Email templates',
+    'sms': 'Text message templates'
 }
 
 

app/templates/main_nav.html

@@ -10,9 +10,9 @@
   </ul>
   {% elif current_user.has_permissions(['manage_templates']) %}
   <ul>
-    <li><a href="{{ url_for('.choose_template', service_id=service_id, template_type='sms') }}">Message templates</a></li>
+    <li><a href="{{ url_for('.choose_template', service_id=service_id, template_type='sms') }}">Text message templates</a></li>
     <li><a href="{{ url_for('.choose_template', service_id=service_id, template_type='email') }}">Email templates</a></li>
-    <li><a href="{{ url_for('.letters_stub', service_id=service_id) }}">Send letters</a></li>
+    <li><a href="{{ url_for('.letters_stub', service_id=service_id) }}">Letter templates</a></li>
   </ul>
   {% endif %}
   {% if current_user.has_permissions(['manage_users', 'manage_settings']) %}

app/templates/views/letters.html

@@ -7,7 +7,11 @@
 {% block maincolumn_content %}
 
   <h1 class="heading-large">
-    Send letters
+    {% if current_user.has_permissions(['send_letters']) %}
+      Send letters
+    {% else %}
+      Letter templates
+    {% endif %}
   </h1>
 
   <p>