OPAL Real Estate has signed a purchase and sale agreement to buy a big chunk of the Clarke Schools for the Deaf in Northampton.  OPAL is owned by Peter Pan Bus magnate Peter Picknelly.  Back in November, Picknelly said the campus' 11 buildings will be converted into 80 luxury apartments.  While Clarke School officials are happy, neighbors are still trying to get historic designation for the property to ensure against what they call architectural disaster.  The 19th century campus is close to Smith College and the city's downtown.