Create DemoArena.

Based on the identified Arena class, the DemoArena subclass is defined. The DemoArena constructor is defined, invoking the parent class constructor, and the code responsible for the layout of directions, orbs, and towers is moved from the Arena constructor to the DemoArena constructor. Finally, a new instance of the DemoArena class is created.To activate Demoarena, right click and select new DemoArena.