[TabPane] Support reordering of Tabs within a TabPane

Summary

Add support for reordering of the tabs within a TabPane.

Problem

Tabs added to a TabPane are displayed in the same sequence as they are added to the TabPane. Once added, the tabs cannot be visually reordered using mouse. It is a very common use case to reorder the tabs in an TabPane based application.

Solution

• Provide an optional property to enable reordering within the TabPane.
• As default behavior the tabs cannot be reordered. This will not alter the behavior of existing applications.
• Fix: http://cr.openjdk.java.net/~arapte/fx/8187074/webrev.08/

Specification

TabDragPolicy property and enum are added to TabPane control:

/**
 * The drag policy for the tabs. The policy can be changed dynamically.
 *
 * @defaultValue TabDragPolicy.FIXED
 * @return The tab drag policy property
 * @since 10
 */
public final ObjectProperty<TabDragPolicy> tabDragPolicyProperty() {}
public final void setTabDragPolicy(TabDragPolicy value) {}
public final TabDragPolicy getTabDragPolicy() {}

/**
 * This enum specifies drag policies for tabs in a TabPane.
 *
 * @since 10
 */
public enum TabDragPolicy {
    /**
     * The tabs remain fixed in their positions and cannot be dragged.
     */
    FIXED,

    /**
     * The tabs can be dragged to reorder them within the same TabPane.
     * Users can perform the simple mouse press-drag-release gesture on a
     * tab header to drag it to a new position. A tab can not be detached
     * from its parent TabPane.
     * <p>After a tab is reordered, the {@link #getTabs() tabs} list is
     * permuted to reflect the updated order.
     * A {@link javafx.collections.ListChangeListener.Change permutation
     * change} event is fired to indicate which tabs were reordered. This
     * reordering is done after the mouse button is released. While a tab
     * is being dragged, the list of tabs is unchanged.</p>
     */
    REORDER
}