Enhance pagination for Matrix Visualizer

[matiasandina]

Using the matrix visualizer with low number of channels gives.

I have been trying to switch pages by clicking or otherwise interacting with the menus available. Without the direct comment for somebody who knew how to do it, I would have never been able to guess that changing pages could be done by pressing Page Up and Page Down keys (it's been 2.5 years!).

Is it possible to add pagination to the menu at the bottom where we can select the number of channels and other great functions for visualizing?

If not, is it possible to better document this?

Given that the current documentation of the MatVisualizer is also missing all other functionalities of the visualizer, maybe in bonsai itself would be a better approach? Even doing it in the title would be good enough and not take anything from the user experience (e.g., "Page 1/10. Move using PgDwn/PgUp")