rest of virtuals removed

virtuals removed and replaced with override where necessary on the rest of the code base, clang-tidy to the rescue.

Engine/source/platform/threads/threadPool.cpp

@@ -206,7 +206,7 @@ struct ThreadPool::WorkerThread : public Thread
    WorkerThread( ThreadPool* pool, U32 index );
 
    WorkerThread*     getNext();
-   virtual void      run( void* arg = 0 );
+   void      run( void* arg = 0 ) override;
 
 private:
    U32               mIndex;