Feature/p2js debug

Okay, I've been able to add a bit more debugdraw support for P2.js. This addresses ekelokorpi/panda.js-plugins#9

 - Compound objects (now showing all shapes in bodies)
 - Rotation support 
 - Offset support 
 - Complex convex shapes

I think there are probably more additions to be made, though in my eyes, these are the first crucial missing debugdraw functions.  

Sample code: 

```
game.module(
    'game.main'
)
.require(
    'plugins.p2'
)
.body(function() {

game.createScene('Main', {
    backgroundColor: 0xb9bec7,

    init: function() {
        this.world = new game.World({gravity: [0, 100]});
        this.world.ratio = 1;

        this.world.solver.iterations = 20;
        this.world.solver.tolerance = 0.001;

        this.world.setGlobalStiffness(1e4);

        // Surface
        var body = new game.Body();
        body.position[0] = game.system.width / 2;
        body.position[1] = game.system.height;

        var bodyShape = new game.Rectangle(game.system.width, 100);
        body.addShape(bodyShape);
        this.world.addBody(body);

        // COMPOUND BODY WITH RECTANGLES AND CIRCLES
        var body = new game.Body({mass: 1});
        body.position[0] = game.system.width / 2;
        body.position[1] = game.system.height / 2;
        body.mass = 1;

        // First rectangle shape
        // Pretty standard rectangle, no rotation
        var bodyShape = new game.Rectangle(50, 100);
        body.addShape(bodyShape, [-200, 0]);

        // Second rectangle shape
        // Pretty standard rectangle, rotation
        var bodyShape = new game.Rectangle(50, 100);
        body.addShape(bodyShape, [200, 100], Math.PI / 4);

        // Third shape, circle this time
        // Offsetted
        var bodyShape = new game.Circle(50);
        body.addShape(bodyShape, [0, -200], Math.PI / 4);

        this.world.addBody(body);

        // POLYGON BODY
        var body = new game.Body({mass: 1});
        body.position[0] = game.system.width / 2;
        body.position[1] = game.system.height / 2;
        body.mass = 1;

        var path = [[-200, 200],
            [-100, 0],
            [100, 0],
            [100, 100],
            [50, 50]];
        body.fromPolygon(path);
        this.world.addBody(body);
    },
    update: function () {
        this._super();
    }
});

});
```