Allow configuration of block size by user

[LnnrtS]

Can be useful to set a tradeoff between throughput and latency.

For example, just running a QCD module alone introduces 20ms latency which is not very useful in that scenario. Lowering the block size would fix that

[danngreen]

Yep, that's a good example for why we need this.
I'm going to close this because it's one of the settings in the Settings Menu issue #184