Feature/codegen (#1480)

* Add the ability to automatically generate code to extract values out of a Dictionary (see https://github.com/openspace/codegen for more information on how to use this)
* Applied this technique to a large number of cases in the codebase
* Don't add _codegen files to the repository

Co-authored-by: Emma Broman <emma.broman@liu.se>

include/openspace/rendering/renderable.h

@@ -61,7 +61,7 @@ public:
     };
 
     static ghoul::mm_unique_ptr<Renderable> createFromDictionary(
-        const ghoul::Dictionary& dictionary);
+        ghoul::Dictionary dictionary);
 
     Renderable(const ghoul::Dictionary& dictionary);
     virtual ~Renderable() = default;