message: Add a Planet::Attributes structure
diff: #include <NAS2D/Resources/Image.h>
  #include <cmath>
  +#include <string>
  class Planet
  @@ -31,6 +32,14 @@ public:
  High
  };
  + struct Attributes
  + {
  + PlanetType type = PlanetType::None;
  + std::string imagePath;
  + int maxDepth = 0;
  + int maxMines = 0;
  + };
  +
  public:
  using MouseCallback = NAS2D::Signals::Signal<>;
  