Appends a new page to the notebook. The widget passed as child will be visible when the page is active, the tab_label will be shown in the tab bar.
If you omit the second tab_label parameter, the default one "page N" (label) will be used.
The method returns the index (starting from 0) of the appended page in the notebook, or -1 if the method fails.
See also: insert_page() , prepend_page() , remove_page()