Marble: Add atmosphere related attributes for celestial bodies
completed by: Mohammed Nafees
mentors: Torsten Rahn, René Küttner
1. Add a new boolean attribute 'atmosphere' to Marble's PlanetPrivate class (in src/lib/Planet.cpp) and a new attribute that holds the atmosphere's color. Provide reasonable default values (set in the constructor). Create appropriate set and get methods in the Planet class that allow access to this new attributes.
2. Modify the atmosphere render plugin (src/plugins/render/atmosphere) in order to use the new attributes for rendering