Changed TextElement in HeaderTemplate to ContentPresenter, in order to allow e.g. Grid, StackPanel as child elment for the header of an Expander control.
Changed TextElement in HeaderTemplate to ContentPresenter, in order to allow e.g. Grid, StackPanel as child elment for the header of an Expander control.

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