TAChart: Add GUI connector for AggPas drawing back-end

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40181 4005530d-fff6-0310-9dd1-cebe43e6787f
TAChart: Use GUI connector in "aggpas" demo

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40182 4005530d-fff6-0310-9dd1-cebe43e6787f