#4635 drop to tree

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36984 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Fixing Auto column header


git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36985 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
#4635 dummy css to indicate target of drag'n'drop

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36986 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e