Provide missing convenience constructors to controls classes

There are a number of constructors that should be considered for addition to the UI controls, to make their use simpler. This is a catch-all for these ideas (so that I can add them in as I encounter them). This does not mean I want to add all of these constructors, it just means that they should be considered.

Here's the list (with the new parameter indicated with <> and comments added with //)

Tab(String title, <Node content>)
Menu(String text, Node graphic, <MenuItem... items>) // Analogous with ContextMenu(MenuItem... items) and SplitMenuButton(MenuItem... items), which both exist
MenuButton(String text, Node graphic, <MenuItem... items>)
SplitMenuButton(<String text>) // These two SplitMenuButton constructors are not available, as they are not inherited from MenuButton (where they exist)
SplitMenuButton(<String text>, <Node graphic>)
TabPane(<Tab... tabs>)
Accordion(<TitledPane... panes>)
MenuBar(<Menu... menus>)
SplitPane(<Node... items>) // analogous to API like ToolBar(Node... items)
TableView(<TableColumn... columns>)
TableView(ObservableList<S> items, <TableColumn... columns>)
TreeTableView(<TreeTableColumn... columns>)
TreeTableView(TreeItem<S> root, <TreeTableColumn... columns>)