Resolved Issue #154 - TableView selectedItem not empty after clearing the selection.

Basically every time an implicit conversion JFX to SFX happened the last item was selected.
Merge remote-tracking branch 'origin/SFX-2'

Conflicts:
	scalafx/src/main/scala/scalafx/scene/control/TableView.scala
	scalafx/src/test/scala/scalafx/scene/control/TableViewSpec.scala