dhb The changes in this commit are to make the right click in the page selector

     more context sensitive.  The intent is to have a menu popup describing the
     window that will be docked or undocked and whether it will be docked or
     undocked.  This works by using treeItemChanged as a slot from the signal
     currentItemChanged from the treeWidget.  After this, we now have the choice
     of removing the virtual functions in the pages class for click and double
     click.