Add block read size as an option to change

[bparks13]

The block read size is an option that can be modified to balance the tradeoff between data reads and throughput. Currently it is hard-coded to be 2048, which is too small when there are multiple Neuropixels devices being recorded from. Shift everything in the editor around so that the read size is underneath the memory monitor.

See if there is an Up/Down editor of some kind, otherwise create a text box for now. If possible, set the step size to be 512 bytes.

Set the default value to be 4096.