widget: Partially unduplicate code for various tab orientations.

Left and right tabs are not used, and may or may not actually work before and/or after this patch.
widget: Remove unused psContext parameter in WIDGET::highlightLost() and replace widgRelease() with delete.
widget: Remove unused major tab tips.
widget: Replace WIDGET::psNext with WIDGET::childWidgets/parentWidget, move most clean up to ~WIDGET().