Allow administrators to configure "Email Settings" settings for lists

Summary:
Fixes T8387. This completes conversion of lists into users.

These settings allow administrators to reduce the amount of mail delivered to lists, ahead of T5791.

Test Plan: {F468206}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8387

Differential Revision: https://secure.phabricator.com/D13138