SvxSimpleTable was a little confused in that it wanted to both
inherit from SvHeaderTabListBox to get list semantics, and to
wrap a SvHeaderTabListBox and HeaderBar inside a single Control

Leading to a chain of events that in some contexts the "Size"
refers to the complete collection of controls, and in some
contexts the "Size" refers to the SvHeaderTabListBox alone.

Split it up, force it to be only a child of SvxSimpleTableContainer and leave
the work of containment to SvxSimpleTableContainer, and leave SvxSimpleTable as
"is a SvHeaderTabListBox" not "is a or maybe has a SvHeaderTabListBox"