Move Zulip's TOS to TERMS_OF_SERVICE markdown file.

This reimplements zulip.com/terms using the new markdown system.

zproject/local_settings.py

@@ -67,6 +67,9 @@ else:
     EXTERNAL_API_PATH = 'api.zulip.com'
     STATSD_PREFIX = 'app'
 
+# Terms of Service
+CUSTOM_TOS = '/etc/zulip/terms.md'
+
 # Legacy zulip.com bucket used for old-style S3 uploads.
 S3_BUCKET="humbug-user-uploads"
 # Buckets used for Amazon S3 integration for storing files and user avatars.