init A4x16 prefab

[another-rishi]

Hi @dbirman,

I created this pull request to facilitate a few questions about adding this new probe.

So far, I've made my prefab and linked the required scripts using the Neuropixels 4-shank probe as an example.

I've added a button for this prefab to the NewProbePanel prefab, but it does not load my prefab when I click it in a build. Is there some other code I need to edit there to test the new probe prefab?

Also, please note that I have not yet made or built the required channel map files. Could that be breaking the new functionality in my build?

Best and thanks for your input, Rishi