Refactor object image creation
Decrease self-repeating in Controller code
Make image size dependent on object radius
Normalize image sizes
Move boundingObject property to OrbitCharacteristics
Add data about Solar System objects
Refactor astronomical objects' fields

Before, mass and radius were optional;
now, they are required for the constructor.
Add null-check for the retrieved object
Create a PhysicalCharacteristics class
Refactor AstronomicalObject content division
Add json-simple library to read text data
Remove flexjson library (impractical approach)
Correct missing return types in Builder class
Implement reading JSON Solar System data
Scale down image size

This is to ensure that any object is visible. Further
scaling is needed (to show even the smallest planets while
not having the Sun cover all the background).