Kinematic bodies cannot be turned into Dynamic bodies

[Ben-G]

I have already briefly discussed this with @jtwigg but want to open issue to keep track of wether implementation will be changed or not.

Currently it is not possible to change the type of a CCPhysicsBody from CCPhysicsBodyTypeKinematic to CCPhysicsBodyTypeDynamic because an assert will be triggered as a result off the formerly Kinematic Body still being in the list of Kinematic Bodies:

    NSSet * tempKinetics = [_kineticNodes copy];
    for(CCNode * node in tempKinetics)
    {
        NSAssert(node.physicsBody, @"Should have a physics body");
        NSAssert(node.physicsBody.type == CCPhysicsBodyTypeKinematic, @"Should be kinematic");

        [node.physicsBody updateKinetics:delta];
        if(node.physicsBody.type != CCPhysicsBodyTypeKinematic)
        {
            [_kineticNodes removeObject:node];
        }
    }

I think it would be useful to be able to change kinematic bodies into dynamic ones. E.g. one could create a throwing animation for a physics body and change the body to be dynamic at the end of the animation.