Gov. Janet Mills and Democratic legislative leaders have unveiled a health care proposal aimed at removing some copayments and combining markets to lower health care costs. The bill would let Maine manage parts of the exchange under the Affordable Care Act, combine the small group and individual markets, and cover yearly primary care and behavioral health visits without deductibles or copays. Its unveiling came as lawmakers returned to work on Wednesday. Democrats have control of both houses of the Maine Legislature and the governorship.