Fix orthographic camera

[RussTedrake]

And demonstrate that it can be constructed via the handle_command interface. This example implements essentially a "planar visualizer" (in the language of drake).

Resolves #3

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This change is 

[RussTedrake]

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test/orthographic_camera.html, line 64 at r1 (raw file):

                path: "/Cameras/default/rotated",
                object: {
                    object: {

btw -- i don't actually really understand why I needed the nested objects here. is that what you would have expected?

[rdeits]

btw -- i don't actually really understand why I needed the nested objects here. is that what you would have expected?

Yeah, it's correct. This is just a slight weirdness of the threejs API, combined with the fact that I use "object" to mean "thing you want to create" and threejs also uses it as a field of the object itself. You can see the same nested object in the set_object API documentation in the Readme.

[rdeits]

Looks great, thanks!