Update default templates and add update command (#166)

This commit adds config_files for default data and, using that, creates a new way to update our default templates without needing to hardcode a migration.

---------

Co-authored-by: Ryan Ahearn <ryan.ahearn@gsa.gov>

app/config.py

@@ -1,6 +1,6 @@
 import json
 from datetime import timedelta
-from os import getenv
+from os import getenv, path
 
 from celery.schedules import crontab
 from kombu import Exchange, Queue
@@ -147,6 +147,9 @@ class Config(object):
     MAX_LETTER_PDF_ZIP_FILESIZE = 40 * 1024 * 1024  # 40mb
     MAX_LETTER_PDF_COUNT_PER_ZIP = 500
 
+    # Default data
+    CONFIG_FILES = path.dirname(__file__) + '/config_files/'
+
     NOTIFY_SERVICE_ID = 'd6aa2c68-a2d9-4437-ab19-3ae8eb202553'
     NOTIFY_USER_ID = '6af522d0-2915-4e52-83a3-3690455a5fe6'
     INVITATION_EMAIL_TEMPLATE_ID = '4f46df42-f795-4cc4-83bb-65ca312f49cc'