LCL: added TControl.ParentVisibleChanged

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@46184 4005530d-fff6-0310-9dd1-cebe43e6787f
LCL: docs

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@46185 4005530d-fff6-0310-9dd1-cebe43e6787f