NEW YORK (Reuters) - The Port Authority of New York and New Jersey on Thursday formally approved rebuilding plans for the site of the World Trade Center destroyed in the September 11, 2001, attacks. The deal with developer Larry Silverstein, approved at the authority's monthly board meeting, gave the developer four and a half years and an additional one-year grace period to complete the building of Towers 2, 3 and 4 on the site, or lose his lease. In addition, the Port Authority agreed to pay Silverstein $300,00O a day if it failed to prepare the site for rebuilding by...