fix(core): Adds Hashed & Hierarchical Timer Wheel (#655)

- Removes TimerPriority
- Removes TimerThread
- Adds a [Hashed & Hierarchical Timer Wheel](http://www.cs.columbia.edu/~nahum/w6998/papers/ton97-timing-wheels.pdf)

Projects/Server.Tests/Fixtures/ServerFixture.cs

@@ -18,12 +18,15 @@ namespace Server.Tests
             // Configure the world
             World.Configure();
 
+            Timer.Initialize(0);
+
             // Load the world
             World.Load();
         }
 
         public void Dispose()
         {
+            Timer.Initialize(0);
         }
     }
 }