Rename parameter in OCP.Toast for consistency with OC.Notification

This fixes HTML messages in "OC.Notification.showTemporary" (as
"showHtml" was not set based on "isHTML"), and also makes OCP.Toast to
keep the old OC.Notification API when used directly.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>