Armstrong Park closed to the public, as indicated by a prominent sign at the entrance. If you've driven past the old Armstrong flooring plant off Plain Street in Braintree lately, you've probably noticed what's been there for decades: chain-link fences, crumbling pavement, and a shuttered factory shell sitting on more than 30 acres of prime South Shore land less than a mile from the Red Line. That's about to change in a big way. National developer Trammell Crow has received P