Settlement Music School, the nation’s oldest and largest community-based music school, dedicated a new campus Thursday in Willow Grove. The $8 million building on Davisville Road has 29 studios and a 320-seat performance hall.  It replaces the Jenkintown campus, which is now closed.  With public schools cutting back on music programs as they try to balance their budgets, Settlement is expanding to serve parents who want their children involved with music.