Added 4 new events (hooks) to PC_user class:
	'PC_user/beforeLogin'
	'PC_user/afterLogin'
	'PC_user/beforeLogout'
	'PC_user/afterLogout'
Fixed a bug when checking for an empty password in PC_user::ChangePassword() method.
Modified PC_user::Send_activation_code() and PC_user::Send_pass_change_code() methods to use PC_utils::sendEmail() method instead of PHPMailer class directly.