Massachusetts officials unveiled a website yesterday to help the public track state spending. The “Open Checkbook’’ website lets the public look up salaries of state workers, see how much is spent on individual contracts with private vendors, and compare budgets of different agencies. Officials warn that the website is still a work in progress. Some data - including budget and spending information for the Massachusetts Port Authority, the Massachusetts Bay Transportation Authority, and quasi-public agencies - have yet to be uploaded. The website does not include budget information from cities and towns.