Make it possible to toggle rendering of a single bot

[NicEastvillage]

Sometimes, especially during bot development, it would be nice to be able to toggle the rendering of specific bots.

Current implementation already associates render groups with a client making it easy to implement (i.e. I am kinda making this PR as a reminder).

Whether this feature needs a keyboard shortcut is something that needs discussion as finding a good shortcut might be challenging (maybe holding page up/down while pressing the number corresponding to the bot index). Alternatively, the toggling is done from the GUI. Adding flatbuffer commands to toggle rendering might be a good idea in any case.