CommonWealth Partners has paid $450 million for the new office tower on Pier 4 in Boston’s surging Seaport District, a record for this year that shows the accelerating demand for the city's historic waterfront that's drawing major corporations from Amazon to General Electric. The 13-story tower at 140 Northern Ave. is 372,372 square feet and is scheduled for completion this month. It’s known simply as Pier 4. CommonWealth, the Los Angeles investment...