JDK-8222258: Add exclusion scope for LightBase

[Nir Lisker]

Hi Kevin/Johan,

I submitted an enhancement request to add an "exclusion scope" to LightBase
[1]. The "exclusion scope" is a list of nodes which should not be affected
by the light. It's a convenient alternative for adding all of the nodes to
the scope except for the ones which should be excluded.

I've written a preliminary Webrev and a sample app that demonstrates the
behavior.

Please evaluate,
Nir

[1] https://bugs.openjdk.java.net/browse/JDK-8222258