fix dock area indicator relative to scene

apply floating property before undocked events generated

Java 9 StageHelper Replacement

The ability to grab all stages was made private in Java 9 so I have to
improvise. My workaround for now is to just maintain a non-threadsafe
package-private statically-initialized list of all DockPanes to use for
scene graph traversal. This works because every Node, which DockPane is
a descendant of, knows its scene which in turn is aware of its stage.

Fix Styleheet

Missed the other method.