DETROIT — The family of an Oxford High senior who died in the mass shooting last fall has filed a lawsuit against Oxford Community Schools and alleges the district violated its own policies and state law in handling concerns about the former student accused of killing four classmates. The family of 17-year-old Justin Shilling and their attorney, Ven Johnson, gathered at a Detroit hotel Monday to discuss a federal lawsuit filed Sunday against the Oakland County school district. Johnson said he will also be adding the family to state court actions. The 40-page complaint alleges the school distri…