TAChart: Extract TBasicPo.FindExtentInterval procedure
+ Minor refactoring.

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40053 4005530d-fff6-0310-9dd1-cebe43e6787f
TAChart: Add TManhattanSeries

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40054 4005530d-fff6-0310-9dd1-cebe43e6787f
TAChart: Add "manhattan" demo

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40055 4005530d-fff6-0310-9dd1-cebe43e6787f