Allow administrators to edit the "Account" panel for mailing lists and bots

Summary:
Ref T8387. Ref T6367. This allows selection of a language, which will be respected in email delievered to the list users.

For example, you could have a German list that gets mail in German or something. I don't know that the feature is really useful, it's mostly just for completeness.

I also supported it for bots, mostly so their pronouns can be configured.

Test Plan: {F468186}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T6367, T8387

Differential Revision: https://secure.phabricator.com/D13136