revert Click on Expander header support (reverted from commit d56c0e5f5052118acc01ae8f2fe7154b82900170)
revert Click on Expander header support (reverted from commit d56c0e5f5052118acc01ae8f2fe7154b82900170)

p76984275/MahApps.Metro,MahApps/MahApps.Metro,batzen/MahApps.Metro,pfattisc/MahApps.Metro,psinl/MahApps.Metro,Jack109/MahApps.Metro,ye4241/MahApps.Metro,Danghor/MahApps.Metro,Evangelink/MahApps.Metro,xxMUROxx/MahApps.Metro,jumulr/MahApps.Metro,chuuddo/MahApps.Metro