A developer that is remaking the Philadelphia skyline plans a $1 billion transformation of a 16-acre swath of the Camden waterfront, the latest in a series of projects spurred on by the promise of state tax incentives for companies that relocate to the city. The plan for what's now a sea of parking lots in one of the nation's most impoverished places calls for 1.7 million square feet of office space in two towers, along with lower-slung buildings including a hotel, 325 housing units, retail and parking garages.