Preview content as hint for broadcast templates

Broadcast services only have broadcast templates. But we show the
template type under the name of the template. This is redundant. It
would be better to preview the content of the template instead.

This then makes the templates page consistent with the dashboard.

Depends on:
- [ ] https://github.com/alphagov/notifications-api/pull/2996

app/__init__.py

@@ -409,7 +409,7 @@ def valid_phone_number(phone_number):
 def format_notification_type(notification_type):
     return {
         'email': 'Email',
-        'sms': 'SMS',
+        'sms': 'Text message',
         'letter': 'Letter'
     }[notification_type]
 

app/models/template_list.py

@@ -1,3 +1,6 @@
+from app import format_notification_type
+
+
 class TemplateList():
 
     def __init__(
@@ -128,12 +131,17 @@ class TemplateListTemplate(TemplateListItem):
     ):
         super().__init__(template, ancestors)
         self.service_id = service_id
-        self.hint = {
-            'email': 'Email template',
-            'sms': 'Text message template',
-            'letter': 'Letter template',
-            'broadcast': 'Broadcast template',
-        }.get(template['template_type'])
+        self.template_type = template['template_type']
+        self.content = template.get('content')
+
+    @property
+    def hint(self):
+        if self.template_type == 'broadcast':
+            max_length_in_chars = 40
+            if len(self.content) > (max_length_in_chars + 2):
+                return self.content[:max_length_in_chars].strip() + '…'
+            return self.content
+        return format_notification_type(self.template_type) + ' template'
 
 
 class TemplateListFolder(TemplateListItem):