Implement World rearrange and add RandomBot and main

Make World::checkEffects non-const and provide its implementation.
Add RandomBot implementation and declare a private randomNumber helper.
Add a simple main() entrypoint.

include/RandomBot.h

@@ -9,4 +9,6 @@ class RandomBot : public BaseRobot {
     public:
         RandomBot ( const int startX, const int startY );
         int mine ( World& world ) override;
+    private:
+        int randomNumber();
 };

include/World.h

@@ -24,7 +24,7 @@ class World {
     void rearrange ();
 
     // stage 3
-    int checkEffects ( int x, int y ) const;
+    int checkEffects ( int x, int y );
 
   private:
     int _sizeX, _sizeY, _sizeZ;