Chunk data to browser

[dylanmcreynolds]

Even if we don't process the data chunk-wise in the browser, it is probably still better for us to send the msgpack blobs in chunks of several MB each rather than a single blob. This might help with the general sluggishness of the browser app.

Assigning to Seij as the harder part of this will be in the browser app. On the server, it won't be all that hard to do.