State Farm has picked a Dunwoody office tower for a 200,000 square foot expansion that could create up to 800 jobs. The nation's largest property and casualty insurance company has signed a five year lease in the Hammond Exchange building, State Farm confirmed. On Jan. 18, Atlanta Business Chronicle first reported on State Farm's planned expansion, identifying Hammond Exchange and The Terraces as potential targets. State Farm declined to discuss details around the expansion, or the reason for…