Make ‘temporary failure’ error less cryptic

‘Phone number doesn’t exist’ as opposed to ‘Permanent failure’ has
tested well because it talks in terms of things people understand.

We should do the same for ‘Temporary failure’, because users are
unclear:
- why this is happening
- if it’s temporary, is Notify going to retry it (it’s not)

We think that ‘Phone/inbox not currently accepting messages’ answers
makes these things clearer.

I’ve reworded it slightly to:

- ‘Inbox not accepting messages right now’
- ‘Phone not accepting messages right now’

app/__init__.py

@@ -235,16 +235,16 @@ def format_notification_status(status, template_type):
         'email': {
             'failed': 'Failed',
             'technical-failure': 'Technical failure',
-            'temporary-failure': 'Temporary failure',
-            'permanent-failure': 'Email address does not exist',
+            'temporary-failure': 'Inbox not accepting messages right now',
+            'permanent-failure': 'Email address doesn’t exist',
             'delivered': 'Delivered',
             'sending': 'Sending'
         },
         'sms': {
             'failed': 'Failed',
             'technical-failure': 'Technical failure',
-            'temporary-failure': 'Temporary failure',
-            'permanent-failure': 'Phone number does not exist',
+            'temporary-failure': 'Phone not accepting messages right now',
+            'permanent-failure': 'Phone number doesn’t exist',
             'delivered': 'Delivered',
             'sending': 'Sending'
         }