Review request for RT-19228

[Greg Brown]

http://javafx-jira.kenai.com/browse/RT-19228

This change adds support for an "fx:constant" attribute that will resolve to the value of a constant (static final variable) defined by the associated element's type. For example:

<TableView> 
    <columnResizePolicy><TableView fx:constant="CONSTRAINED_RESIZE_POLICY"/></columnResizePolicy> 
</TableView> 

It parallels the fx:value and fx:factory attributes, which are used to invoke a static valueOf() method and an a static factory method on the target type, respectively.

Greg