8u API Review request: RT-153 : [Stage] Option to keep Stages always on top

[Martin Sladecek]

Steve, Kevin,

please review:
https://javafx-jira.kenai.com/browse/RT-153
http://cr.openjdk.java.net/~msladecek/rt-153/webrev.00/ 
<http://cr.openjdk.java.net/%7Emsladecek/rt-153/webrev.00/>

The only API change is adding alwaysOnTop property to Stage, which 
includes the following methods:

public final void setAlwaysOnTop(boolean value);
public final boolean isAlwaysOnTop();
public final ReadOnlyBooleanProperty alwaysOnTopProperty();

Thanks,
-Martin