make debugDrawWorld virtual for btSoftRigidDynamicsWorld

Move btSoftBodyWorldInfo to public, instead of nested, so it can be easier forward declared.
See http://code.google.com/p/bullet/issues/detail?id=78

Add get methods for damping/thresholds, see http://code.google.com/p/bullet/issues/detail?id=77

Demos/SoftDemo/SoftDemo.h

@@ -49,7 +49,7 @@ public:
 
 	btAlignedObjectArray<btSoftRididCollisionAlgorithm*> m_SoftRigidCollisionAlgorithms;
 
-	btSoftBody::btSoftBodyWorldInfo	m_softBodyWorldInfo;
+	btSoftBodyWorldInfo	m_softBodyWorldInfo;
 
 	
 	bool								m_autocam;