Replace blue boxes with total + delivery estimate

The sending/failed/delivered thing:
- doesn’t map to the actual states of letters
- doesn’t respond quickly enough to give you feedback that something is
  happening (because "sending" doesn’t even go to "probably delivered"
  for a few days)

This commit replaces these 4 boxes with some more useful information:
- one number – how many letters were in the job in total
- when we estimate that the letters will be delivered

tests/app/main/views/test_jobs.py

@@ -177,6 +177,12 @@ def test_should_show_letter_job(
     assert normalize_spaces(page.select('tbody tr')[0].text) == (
         '07123456789 template content'
     )
+    assert normalize_spaces(page.select('.keyline-block')[0].text) == (
+        '1 Letter'
+    )
+    assert normalize_spaces(page.select('.keyline-block')[1].text) == (
+        '6 January Estimated delivery date'
+    )
 
     mock_get_notifications.assert_called_with(
         SERVICE_ONE_ID,