Improve download throughput

[Markus-Goetz]

The current version of the download method limits the throughput at a maximum of 40 KB/s (due to chunk size and the sleep). The fix increases the chunk size so 16 KB, factors it out as a class member and remove the sleep in order to allow for maximum possible throughput

[renefritze]

Would it be possible to get this merged and released @drdarshan ?

[mjacobse]

I'd appreciate that too, working with large matrices is pretty impractical in the current state. And to a user it might not be immediately obvious that they are waiting because of artificially throttled download speed, took me a moment to realize.