UI: support for new planet / star textures

Star type will now be generated from fixed list, each w/
corresponding texture. At some point would be worth
investigating using a base texture and mix it with the star color
via the material.

Also adds rgb color uniforms to star glow shader & set during
star initialization

Tests / specs need to be updated to reflect new/changed
functionality
UI: handle first system click differently than second

First click: focus on system, bring up details, refresh
Second click: set scene root, current functionality

Tests need to be updated to reflect new functionality
UI: fix broken tests