Fixes in registration pipeline

[georgelgeback]

• Fix empty stil-id being rejected when registering!!
• Add clearing of stil-id to user edit route, previously it would see a falsy value and avoid updating
• Update email-in-password check to reject based on the first part of the email (cool_name@example.com can now reject password if cool_name is in it), previously the whole email had to be a substring for the password to be rejected

Added unit regression tests for these three