Added basic "flyCameraTo" method

I added a couple methods we can use later on.

The first is just a test method to get us some simple objects in the universe to fly between (they're not added to the simulation).
Use addTestBodies(numBodies, minSize, maxSize, distance) to throw some random spheres into the scene. They'll be accessible in scene.children.

Then, you can use, for example, flyCameraTo(scene.children[3], 2000) to move to that mesh in 2000 ms. It's simple fixed velocity now, but can add acceleration/deceleration later.