DisplayWebgl: modified object storing: now bodies are stored and they are grouped into objects with body_id reference (this way bodies can be reused and more object instances can be created with different parameters), objects that need render are now in objects_to_render
World demo: updated world_demo.js to use the DisplayWebgl as it is at 96ef5075982b8aee71ec33b26d97f9ec767cfca7
Merge pull request #20 from gheja/world

World