Let users search for letters

Like we have search by email address or phone number, finding an
individual letter is a common task. At the moment users are having to
click through pages and pages of letters to find the one they’re looking
for.

We have to search in the `to` and `normalised_to` fields for now because
we’re not populating the `normalised_to` column for letters at the
moment.

app/dao/notifications_dao.py

@@ -26,7 +26,6 @@ from werkzeug.datastructures import MultiDict
 from app import db, create_uuid
 from app.aws.s3 import remove_s3_object, get_s3_bucket_objects
 from app.dao.dao_utils import transactional
-from app.errors import InvalidRequest
 from app.letters.utils import get_letter_pdf_filename
 from app.models import (
     FactNotificationStatus,
@@ -600,11 +599,8 @@ def dao_get_notifications_by_recipient_or_reference(service_id, search_term, not
         except InvalidEmailError:
             normalised = search_term.lower()
 
-    elif notification_type == LETTER_TYPE:
-        raise InvalidRequest("Only email and SMS can use search by recipient", 400)
-
     else:
-        normalised = search_term.lower()
+        normalised = ''.join(search_term.split()).lower()
 
     normalised = escape_special_characters(normalised)
     search_term = escape_special_characters(search_term)
@@ -612,6 +608,7 @@ def dao_get_notifications_by_recipient_or_reference(service_id, search_term, not
     filters = [
         Notification.service_id == service_id,
         or_(
+            Notification.to.ilike("%{}%".format(search_term)),
             Notification.normalised_to.like("%{}%".format(normalised)),
             Notification.client_reference.ilike("%{}%".format(search_term)),
         ),