Provide buffer-proxy interface arguments for blitz clients

[jmoore]

Once insight and importer switch to using blitz, it may make significant sense to offer parallel methods to take and return ByteBuffer, IntBuffer, ... proxies which could be passed all the way to/from OmeroFs or any other store (e.g. for historgrams or projections).

Another alternative would be to have clients pass in ByteBufferCallBacks, so that the server handles the for-loop.

Whatever metaphor we implement, passing proxies from as close to the source of binary data to as close to the consumers as possible will increase performance.