The House sponsor of Rhode Island's medical marijuana law, Rep. Thomas Slater, passed away today after a long battle with cancer.  In addition to championing the needs of seriously ill patients who could benefit from medical marijuana, he was the tireless advocate of the needy in his district, from driving elderly constituents to the pharmacy or supermarket to sponsoring legislation for health care for uninsured children and affordable housing. In June, the Providence Journal published a moving profile…