Node inspector

I was sad that calling #inspect on Java FX objects didn't return much useful information.

This pull only deals with `#inspect` on objects descended from `Node`. It is able to discover all the properties of just the top class. (It can be used for more custom inspections, see `inspector_spec`)

    Java::JavafxSceneShape::Rectangle.new.inspect => 
      #<Java::JavafxSceneShape::Rectangle:0x64027866 x:0.0 y:0.0 width:0.0 height:0.0 arcWidth:0.0 arcHeight:0.0>

Lots of examples in the specs.

I'd like to get a useful inspect for Events as well, someday.

Enjoy!

*dirty: https://github.com/whitehat101/jrubyfx/tree/inspector*