Refactor to split s3_client.py into multiple files

Separated s3_client.py into 3 files - for logos, CSV files and the MOU.
This helps to keep things clearer now that we need to add lots more logo
functions for letters.

app/main/views/agreement.py

@@ -2,8 +2,8 @@ from flask import abort, render_template, request, send_file, url_for
 from flask_login import login_required
 
 from app.main import main
-from app.main.s3_client import get_mou
 from app.main.views.sub_navigation_dictionaries import features_nav
+from app.s3_client.s3_mou_client import get_mou
 from app.utils import AgreementInfo
 
 

app/main/views/email_branding.py

@@ -4,7 +4,7 @@ from flask_login import login_required
 from app import email_branding_client
 from app.main import main
 from app.main.forms import SearchTemplatesForm, ServiceUpdateEmailBranding
-from app.main.s3_client import (
+from app.s3_client.s3_logo_client import (
     TEMP_TAG,
     delete_temp_file,
     delete_temp_files_created_by,

app/main/views/send.py

@@ -42,7 +42,11 @@ from app.main.forms import (
     SetSenderForm,
     get_placeholder_form_instance,
 )
-from app.main.s3_client import s3download, s3upload, set_metadata_on_csv_upload
+from app.s3_client.s3_csv_client import (
+    s3download,
+    s3upload,
+    set_metadata_on_csv_upload,
+)
 from app.template_previews import TemplatePreview, get_page_count_for_letter
 from app.utils import (
     Spreadsheet,