MLG restaurant in downtown Jacksonville has closed, with a source familiar with the business telling the Business Journal its last day of operation was Mother's Day. The source said that owner Marcus Lemonis "no longer wanted to invest money into the business," which opened six months ago. Wednesday evening, the restaurant was completely blocked off with a sign saying "exciting changes coming!" The second location of a Chicago-based "upscale New American style" restaurant, MLG is owned by Lemonis,…