can link/unlink slave to master
can show element by double clic item on the list
reset modification
git-svn-id: svn+ssh://svn.tuxfamily.org/svnroot/qet/qet/trunk@2878 bfdf4180-ca20-0410-9c96-a3a8aa849046
add slave element class.
element class: replace diagramcontext informations by elementInformations because informations is already used in xml file for element.
minor improvement.
git-svn-id: svn+ssh://svn.tuxfamily.org/svnroot/qet/qet/trunk@2869 bfdf4180-ca20-0410-9c96-a3a8aa849046