added labels to bodies, constraints and composites

src/body/Body.js

@@ -22,6 +22,7 @@ var Body = {};
         var defaults = {
             id: Body.nextId(),
             type: 'body',
+            label: null,
             angle: 0,
             position: { x: 0, y: 0 },
             force: { x: 0, y: 0 },

src/body/Composite.js

@@ -27,7 +27,8 @@ var Composite = {};
             isModified: false,
             bodies: [], 
             constraints: [], 
-            composites: [] 
+            composites: [],
+            label: null
         }, options);
     };
 

src/body/World.js

@@ -20,6 +20,7 @@ var World = {};
         var composite = Composite.create();
 
         var defaults = {
+            label: 'World',
             gravity: { x: 0, y: 1 },
             bounds: { 
                 min: { x: 0, y: 0 }, 

src/constraint/Constraint.js

@@ -54,6 +54,7 @@ var Constraint = {};
 
         // option defaults
         constraint.id = constraint.id || Constraint.nextId();
+        constraint.label = constraint.label;
         constraint.type = 'constraint';
         constraint.stiffness = constraint.stiffness || 1;
         constraint.angularStiffness = constraint.angularStiffness || 0;

src/constraint/MouseConstraint.js

@@ -20,6 +20,7 @@ var MouseConstraint = {};
         var mouse = engine.input.mouse;
 
         var constraint = Constraint.create({ 
+            label: 'Mouse Constraint',
             pointA: mouse.position,
             pointB: { x: 0, y: 0 },
             length: 0.01,