Attorney Martha Coakley is calling for a hike in the minimum wage, universal pre-kindergarten and earned sick time for all Massachusetts workers as she stumps for the Democratic nomination for governor. Coakley made the pitch Thursday at a speech before the Greater Boston Chamber of Commerce. She also pledged to tackle income inequality, echoing a theme embraced by President Barack Obama. Coakley said the difference between the haves and the have-nots is stark across the country, but it is among the sharpest in Massachusetts. She said guaranteeing earned sick time will help ease workers' fears of losing wages or their job if they have to stay home sick or to care a family member. She said universal pre-kindergarten will help close the achievement gap in schools.