Now toolbarview always compute up-to-date sizes and spacing to adapt to
changes in icon big font.
For treeview and toolbarview revert the goto_size approach to use the
original approach of rxi/lite. In order to make it work when user resizes
dragging the divider we use the view optional method set_target_size().
This latter changes the view's target size instead of changing its size
right away. The size is only changed by the lite's layout and animation
system.
Remove the config.treeview_size variable that was no longer working because
plugins are loaded before the user's config.
Francesco Abbate