Login with e-mail address is case-sensitive

[jannislehmann]

Describe the bug
When trying to log in using an e-mail address, the e-mail has to be case-senstive.

To Reproduce

1. Create a user with an e-mail
2. Try to log in with any character in uppercase.

Expected behavior
The e-mail address should be handled case-insenstive.

[vladisalv]

++

Also, please, strip spaces in e-mail

[JetForMe]

This is a regular problem for me, as users on mobile generally end up with the first letter auto-capitalized. I'll open a separate bug about setting the field type.