Stage properties fullScreen and iconified must be non-bindable

The Stage properties "fullScreen" and "iconified" must be non-bindable. In both cases, they are properties that can be modified in response to end-user actions which are external to the application. The runtime must be able to set their values in response to these external actions.

There are two choices.

1) We can extend the pattern used by Window for the x, y, width, height properties and create an internal NonBindableBoolean class which will throw a RuntimeException if an application attempts to bind to them.

2) We can change the pattern for these two and for Window x, y, width, height such that the properties are defined as ReadOnlyProperty with a public set method. The latter pattern is a better choice since it prevents the users from binding to them at compile time rather than relying on a runtime exception. I will file a new issue for this.