Make user emails case-insensitive

Summary: Ref T1191. Same deal as D10786. These were previously case-insensitive, but changed to a case-sensitive column type.

Test Plan: Ran `bin/storage adjust` and got and adjustment.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: webframp, epriestley

Maniphest Tasks: T1191

Differential Revision: https://secure.phabricator.com/D10806