Change usernames to `sort64` to make them case-insensitive

Summary: Ref T1191. After adjustment, usernames currently end up case-sensitive, which means `alincoln` and `Alincoln` are different users. Make them case-sensitive so these names collie.

Test Plan: Ran `bin/storage adjust`.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T1191

Differential Revision: https://secure.phabricator.com/D10786