Add asynchronous loading of textures and buffers to Dragon render aspect

Steps to perform this task:

1. On each type that holds loaded data, such as LoadedBuffer, add a QFuture that holds the data.
2. In the loading function, add a concurrent call to function that loads the data and store the result in the QFuture.
3. In the loading function (or in a separate function that is added next in the task pipeline) such as loadBuffers, add a step that goes through all existing loaded buffers and checks if the QFuture has completed.
4. If completed, move the result of the future to the data member of LoadedBuffer and put the resulting LoadedBuffer into the value container.