TitledPane: setTitle(Node) and TitledPane(Node, Node) should be changed to setText(String) and TitledPane(String, Node)

Justification: Currently the TitledPane API differs from the Tab and TableColumn APIs. TitledPane requires a Node for the title area, whereas Tab and TableColumn provide text/graphic as separate APIs. These are simpler to work with, especially in the common case of just setting text strings. We should have one constant style for Tab, TitledPane's Title and TableColumn.

Overview of changes: TitledPane's api for title should be changed to have text and graphic properties. The title property should be removed. The constructors should be updated as appropriate.