logging in with email #163
Description
context: users can login with their emails.
other context: shari will use her own email for two different accounts (her personal account + customers account that redirects user to customer pages) as well as glen using his own email for his personal account and volunteers.
change logging in logic so that code searches for the matching email + password pair instead of failing when password for an email is not matched
side change: take care of error messages (can make it more generic to say email/user and password pair not found)