addPage
Adds @child to @self with @parent as the parent.
This function can be used to automatically position new pages, and to select the correct page when this page is closed while being selected (see method@TabView.close_page).
If @parent is NULL, this function is equivalent to method@TabView.append.
Return
the page object representing @child
Parameters
child
a widget to add
parent
a parent page for @child