HiDPI in monocle

[Johan Vos]

Hi,

With the changes introduced in the fix for RT-27960 (
https://bugs.openjdk.java.net/browse/JDK-8098184), the hidpi support on
Android is broken.

As part of the changes in
http://hg.openjdk.java.net/openjfx/8u-dev/rt/rev/670ed25ed138, we
introduced a getScale method on NativeScreen, and the result of this method
was used in the constructor of Screen (See MonocleApplication.java). As an
example, on a Nexus 5 the getScale() would return 3.0, as the device has
1920x1080 physical pixels but we use a Scene with dimensions 640x360.

I'm not sure how to map this getScale() to the new getPlatformScale() and
getRenderScale() though?

- Johan