[API Review]: Add "margin" property to node and make it styleable from CSS

[Martin Sladecek]

Hi,

JIRA issue: https://javafx-jira.kenai.com/browse/RT-27785
This API change is about adding marginProperty() to Node that would be 
then used by layout Panes instead of the current constraints (static 
methods getMargin/setMargin). The getMargin/setMargin on these Panes 
will just delegate to the property.

Unfortunately, it's not possible to update Region.layoutInArea and 
Region.positionInArea methods to use child.getMargin() internally, as 
there's an overloaded method (in both cases) that already doesn't have 
Margin in it's parameters and uses Insets.EMPTY instead. Changing this 
to child.getMargin() might cause backward incompatibility issues.

Thanks,
-Martin