[API Review] RT-20906: Support setting min/pref/max sizes via css

[David Grieve]

This issue isn't going to introduce new Class members, but it does affect what is specifiable from CSS and thus requires an API review. Implementation of this API will require changes to javafx.scene.layout.Region to fit the corresponding height and width properties into the CSS framework, but these changes wouldn't affect 't the Region API.

http://javafx-jira.kenai.com/browse/RT-20906

-fx-min-width: <length> 
-fx-min-height: <length> 
-fx-pref-width: <length> 
-fx-pref-height: <length> 
-fx-max-width: <length> 
-fx-max-height: <length> 

<size> is defined in http://docs.oracle.com/javafx/2/api/javafx/scene/doc-files/cssref.html#typelength 

Percentage values are not allowed since the actual value would need to be computed from the width and/or height of the Node's parent before the parent is laid out.