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/s3_client/s3_logo_client.py

@@ -0,0 +1,74 @@
+import uuid
+
+from boto3 import resource
+from flask import current_app
+from notifications_utils.s3 import s3upload as utils_s3upload
+
+TEMP_TAG = 'temp-{user_id}_'
+LOGO_LOCATION_STRUCTURE = '{temp}{unique_id}-{filename}'
+
+
+def get_s3_object(bucket_name, filename):
+    s3 = resource('s3')
+    return s3.Object(bucket_name, filename)
+
+
+def delete_s3_object(filename):
+    bucket_name = current_app.config['LOGO_UPLOAD_BUCKET_NAME']
+    get_s3_object(bucket_name, filename).delete()
+
+
+def persist_logo(old_name, new_name):
+    if old_name == new_name:
+        return
+    bucket_name = current_app.config['LOGO_UPLOAD_BUCKET_NAME']
+    get_s3_object(bucket_name, new_name).copy_from(
+        CopySource='{}/{}'.format(bucket_name, old_name))
+    delete_s3_object(old_name)
+
+
+def get_s3_objects_filter_by_prefix(prefix):
+    bucket_name = current_app.config['LOGO_UPLOAD_BUCKET_NAME']
+    s3 = resource('s3')
+    return s3.Bucket(bucket_name).objects.filter(Prefix=prefix)
+
+
+def get_temp_truncated_filename(filename, user_id):
+    return filename[len(TEMP_TAG.format(user_id=user_id)):]
+
+
+def upload_logo(filename, filedata, region, user_id):
+    upload_file_name = LOGO_LOCATION_STRUCTURE.format(
+        temp=TEMP_TAG.format(user_id=user_id),
+        unique_id=str(uuid.uuid4()),
+        filename=filename
+    )
+    bucket_name = current_app.config['LOGO_UPLOAD_BUCKET_NAME']
+    utils_s3upload(
+        filedata=filedata,
+        region=region,
+        bucket_name=bucket_name,
+        file_location=upload_file_name,
+        content_type='image/png'
+    )
+
+    return upload_file_name
+
+
+def permanent_logo_name(filename, user_id):
+    if filename.startswith(TEMP_TAG.format(user_id=user_id)):
+        return get_temp_truncated_filename(filename=filename, user_id=user_id)
+    else:
+        return filename
+
+
+def delete_temp_files_created_by(user_id):
+    for obj in get_s3_objects_filter_by_prefix(TEMP_TAG.format(user_id=user_id)):
+        delete_s3_object(obj.key)
+
+
+def delete_temp_file(filename):
+    if not filename.startswith(TEMP_TAG[:5]):
+        raise ValueError('Not a temp file: {}'.format(filename))
+
+    delete_s3_object(filename)