Querki shouldn't be treating email addresses as case-sensitive!

Summary: Currently, if you create your account with non-lowercase letters (Foo@Bar.com), that gets enforced pretty much forever -- if you try signing in as foo@bar.com, it won't work, because the encryption won't match. This is broken, since almost every system in the world treats email addresses as case-insensitive.

Noticed by Courtney.

Not obvious what the right fix is, given that we already have some users whose login hashes were built around case-sensitive email addresses. Likely we should begin to force lowercase both at signup and login, but we need to keep checking the literal given form when someone is signing in, at least for the moment.

I believe this problem is also true of handles.