Bugfix/login case

[CarvellWakeman]

NOTE: This branch needs one more change before being merged. We are waiting on an email template to include in the username -> email migration. DO NOT merge until this notice is removed.

Fixes issue #596

Changes in this PR.

This branch introduces fixes for the login page, add account and edit account pages when it comes to username and email address uniqueness, case, and whitespace. It replaces the built in backend authenticator in order to ignore case when logging in.
Due to this, there cannot be any duplicate users in the system. This includes by case. Two users with email addresses "[email protected]" and "[email protected]" will not allow either user to log in.

** BEFORE THIS IS MERGED **
The environments where this is being applied MUST have duplicate users removed.
I have already identified users in prod data which are duplicates, they are attached to the issue this fixes.

Testing this PR.

1. With existing and new users, try to log in with several variations of case and whitespace with both usernames and email addresses.
2. Try to edit and add new accounts with duplicate email addresses or usernames, as well as usernames and email addresses with variations in case and whitespace.
3. There should never be two users with the same email address or usernames (assuming both have whitespace removed and are lowered)