Adds a page and its associated tab with the given label to the widget.
While you can still use the addTab from the parent class, *strongly* recommend you use addPage insteaad.
Gets the page at the given tab index, or null if the index is bad.
Adds the a new tab to the control with the given title.
Tabs can change existing content or can be new pages.
When the user picks a different tab, a change message is generated.
A tab widget is a set of clickable tab buttons followed by a content area.