Added test for custom scroll area skin

git-svn-id: https://www.libavg.de/svn/trunk/libavg@9015 44470bb9-56e9-0310-a0f8-c586564d3dc6
Updated test media

git-svn-id: https://www.libavg.de/svn/trunk/libavg@9016 44470bb9-56e9-0310-a0f8-c586564d3dc6
Cherry picked for custom scrollbar skinObject from libavg_dena branch

git-svn-id: https://www.libavg.de/svn/trunk/libavg@9017 44470bb9-56e9-0310-a0f8-c586564d3dc6