Implement planetary asset streamer

[aggregate1166877]

Details:
We need something to stream in images and height data for celestial bodies. This would be akin to something like tile servers used by OpenStreetMap and Google Maps.

Example use case:

• When far away, planet is a sprite mimicking relative luminosity.
• Stream in higher quality images as you get closer to a planet, eventually getting very detailed.
• Once close enough, start streaming in heightmap info to give the planet terrain as as well.

This might might take form as a separate application service spawned by the main application.