update image system page

[magbaeta]

This is a suggested image for the main (first) page of ONIX documentation.

[cjsha]

This is how this looks.

Here are my notes:

• might be worth captioning on what's on each of the three setups
• though the entire image itself is about the right size, each of the three setups themselves feel kinda small
• if you have quick access to animal data, it would be nice to use screenshots that are created streaming animal data (use the new ephys tester board? but then all channels are the same).
• is there some uncanny about the photoshopping of the screenshots? maybe not. might be ok.

What do you think? @ChucklesOnGitHub @magbaeta