PhysicExporter update, updated flags in Cache & Loader

Hi added the ability to retrieve a single fixture from the cache. This becomes handy when you want to create some manual p2 bodies. I currently use it to maintain a list of circle sensors in Physics Editor. So I can maintain position, radius, mask bits, category bits and the sensor flag with PhysicsEditor.

Here an example to manually create a single sensor body:
```javascript
    p2world = game.physics.p2
    sensorFixture = game.cache.getPhysicsData('physics', 'mySensors', 'singleSensorFromTheList')
    // [0,0] is the default position of a body
    ///You should set the position to (x - width/2) and (y - width/2) of the sprite this fixture was designed for in physics editor.
    body = new p2.Body(position:[0,0])
    //The retrieved fixture is a circle, so access it with the circle property
    shape = new p2.Circle(p2world.pxm(fixture.circle.radius)) 
    
    //these are set in PhysicsEditor via the bit field- so I do not have to manage them in Phaser
    shape.collisionGroup = fixture.filter.categoryBits
    shape.collisionMask = fixture.filter.maskBits
    shape.sensor = shape.isSensor
    //the offset inside the body. This is easy for a circle. For a polygon you have to calcualte the mass center. See phaser's p2 body how to do it in case you want to create a manual polygon.
    offset = fixture.circle.position
    offset[0] = p2world.pxmi(offset[0])
    offset[1] = p2world.pxmi(offset[1])

    body.addShape(shape, offset)
    p2world.world.addBody(body)
    debugBody = new Phaser.Physics.P2.BodyDebug(game, body)
```