For years, the old stone house beside a Montgomery County farm field was largely forgotten. It was swallowed by forest, marred by graffiti and crumbling to the earth. But now, partially restored and easily accessible, it is the centerpiece of Maryland’s newest state park. The 1,042-acre Freedman’s State Park near Gaithersburg honors the legacy of the Howard family, who owned the land after emancipation from slavery, and became major contributors…