Fix transforms not working with physics composites objects

[leruaa]

This PR is my second attempt to fix the issue #81 after the PR #88.

I followed your instructions to compute global coordinates recursively :

The way this properly should be fixed is - when positioning the box2d item in physics system, we should position it using not local coordinates, but global coordinates calculation (by recursively going up through parents)

[azakhary]

Thanks!