webui: login screen - improved button switching
- added cancel button to reset password view of login screen
- re-implemented buttons hiding mechanism
- switching between 'Reset Password' and 'Reset Password and Login' according to presence of value in OTP field
https://fedorahosted.org/freeipa/ticket/4470
Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>