From Bertrand:

- a tab has been added, allowing to edit queries without the need to
  open "edit query" dialog.
- remember which packages were enabled in a particular session and
  automatically re-enable them when restarting that specific session.
- allow double click to open session (with changes in TGListTree).


git-svn-id: http://root.cern.ch/svn/root/trunk@13293 27541ba8-7e3a-0410-8455-c3a389f83636