Few changes to column headings for clarity

- Removed "Failed" and "Total costs" on jobs page
- Changed "Sent" to "Processed" on jobs page.
- Removed "sent" from dashboard page on jobs table.

tests/app/main/views/test_jobs.py

@@ -74,9 +74,8 @@ def test_should_show_updates_for_one_job_as_json(
 
         assert response.status_code == 200
         content = json.loads(response.get_data(as_text=True))
-        assert 'sent' in content['counts']
+        assert 'processed' in content['counts']
         assert 'queued' in content['counts']
-        assert 'failed' in content['counts']
         assert 'Recipient' in content['notifications']
         assert 'Status' in content['notifications']
         assert 'Started' in content['status']