Fix a bug in delete

* Don't expand nodes by default
* Distinguish notification types from document to view
  ( update of one item, global change, append of one item)
* Handle item-append 
   - Add a command/callback
   - TODO: Only rebuild the tree image if the newly appended item is 
     visible
* Rename m_lastPos to m_firstPos as it represents the first position
* Beginning of a general ensureVisible function (not working yet)

by a simple click (was a double click before) which is more
natural

 (at the moment the tree control is still entirely rebuilt,
 but now it will be easier to fix that)
 + coding style fixes

 * skins2/vars/playtree.cpp: removed some debug lines

   work, cleaning and fixing. I'll continue this weekend.