Jessica A. O'Brien wants to talk business.“The legal profession, in the private sector at least, it’s still a business,” O’Brien said. “It’s rainmaking. It’s what keeps you working for a firm.”With that in mind, O’Brien will honor four businesswomen Thursday at her installation as the Women’s Bar Association of Illinois’ 99th president: Patricia A. Hemingway Hall, president and CEO of Health Care Service Corp.; Theresa E. Mintle, president and CEO of the …