Extract formatters into their own module

We have lots of functions for converting various types of data into
strings to be displayed to the user somewhere.

This commit collects all these functions into their own module, rather
than having them cluttering up `app/__init__.py` or buried amongst
various other things that have ended up in `app/utils.py`.

tests/app/main/views/uploads/test_upload_hub.py

@@ -4,7 +4,7 @@ import pytest
 from flask import url_for
 from freezegun import freeze_time
 
-from app.utils import normalize_spaces
+from app.formatters import normalize_spaces
 from tests.conftest import (
     SERVICE_ONE_ID,
     create_active_caseworking_user,