cody: lvlgraph: highlight node under mouse

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40311 4005530d-fff6-0310-9dd1-cebe43e6787f
cody: lvlgraph: highlight node under mouse

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40312 4005530d-fff6-0310-9dd1-cebe43e6787f