Implemented gtk_extended_layout_is_height_for_width() and added another guess algorithm

Implemented gtk_extended_layout_is_height_for_width() and added another guess algorithm

This patch adds another commented algorythm to find the collective
minimum and natural height for a said width of a horizontally oriented
box (or the opposite). The algorithm works quite well and can be optimized
a bit more - currently its commented because GtkLabel cannot effectively
do width-for-height calculations (doh).

Further, this patch returns an is_height_for_width() preference depending
on the boxes orientation (vertical boxes are width-for-height).