Republican gubernatorial candidate Walker Stapleton outlined health care proposals Tuesday that would seek to better integrate mental health services into the primary care system, rein in Medicaid spending and allow for lower-cost insurance plans, including some providing less coverage. Stapleton, the state treasurer, said his plans would simplify and streamline health care, while providing more options — including allowing healthy young people to buy “catastrophic” insurance plans that no longer are allowed under the basic insurance requirements of the Affordable Care Act.