Fixed issues and bugs

-moved system destroy functionality to System structure "destroy()" function
-now arrays are properly destroyed (with destructor calling (__xdtor))
-fixed bug which makes BlockAllocator crashing after freeing it's memory
-fixed many smaller memory leaks

source/bubel/ecs/block_allocator.d

@@ -54,6 +54,7 @@ struct BlockAllocator
             Mallocator.dispose(pointers);
             pointers = next_pointers;
         }
+        next_block = null;
     }
 
 private: