Implement celestial lighting

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[Parent issue: #74]

Details:
We need to make planets and the space ship interiors respect local star light.

Task:

• Implement a mechanism to differentiate between stars, light emitting planets, and regular planets.
• Make stars light emitters.
• Give celestial bodies the materials needed to facilitate lighting.
• Ensure the space ship itself has realistic shadows.

Note that this task refers to lighting from the local star and does not include stars that are light years away.

Investigation to be followed in comments below.

[aggregate1166877]

Investigation 1:
Naively create a light emanating from the Sun hitting the Earth.

Result:
We may need a few hacks to make this work nicely. Initial code written using traditional methods tank the framerate to 1FPS, and shadows don't work well over long distances. This likely because our scene is literally millions of kilometers wide (to scale, in meters) simply going from Sun to Earth, never mind beyond.

Putting this task on hold for now because it would be easier to implement at a later stage (such as when we have debugging menus/etc readily available).

[aggregate1166877]

Investigation 2:
Check if it's possible to isolate lighting between scene children. For example, in a parent -> child1, parent -> child2 setup, does a hemi light from child1 affect child2? If not, we could possibly set up hemi light for sun -> planets, a directional light for sun -> ship, and do some hacks such as fading ship light gradually the more a planet intersects of path to the sun.

Result:
Turns out if you add a light anywhere in a scene, it affects anything with castShadow or receiveShadow. The engine does not support layering within scenes. However - you can create two completely different scenes, and pass both through the same renderer. One is superimposed over the other, both exist physically in the same space, but visually looks identical. And light created in scene1 does not affect scene2.

Great success. Although not quite - it seems this breaks post-processing (likely related to mrdoob/three.js#1017). Right now I think lighting is more important because without it the game would be complete potato. Can't have that. Hopefully we find a work-around for the post-processing issues.

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Initial lighting is working very nicely. Light values are currently hard-coded, though.

To make things realistic, we need to be able to do things like calculating distance to nearest star, adjust star color by class, etc. This is currently not possible because all planetary bodies are currently generated using hard-coded JSON.

Putting this on hold until #55 is resolved.