Review request for JMC-6277: Supporting new JavaFX 12 events

[Marcus Hirt]

Hi all,

Please review this fix to support the new JavaFX 12 events.
See:    https://bugs.openjdk.java.net/browse/JDK-8088418

Included are also some fixes for minor warnings and mounting
the metadata and g1 optional pages plug-ins in better places.

Jira:   https://bugs.openjdk.java.net/browse/JMC-6277
Webrev: http://cr.openjdk.java.net/~hirt/JMC-6277/webrev.01/

Kind regards,
Marcus