Image fetch responses are serialized multiple times unnecessarily

[jdm]

When an image element requests an image, it starts a fetch and then feeds the fetch response to the image cache chunk by chunk. This means that the network thread serializes the response data in order to send it to the listener, and the listener serializes the data again in order to send it to the image cache. It would be much more efficient if the image cache were the direct listener for the fetch operation instead.