Picochess V4 interchangeable book

[Antonio]

Hello Picochess friends! The program is now more configurable. We can play against an engine using a specific opening book while being "guided" by a different one, and we can switch between them at any point during the game. What do you think of the idea?

https://www.youtube.com/watch?v=ccJtZZtxhkQ

[Johan Sjöblom]

I have opened an issue https://github.com/JohanSjoblom/picochess/issues/202

and branch: 202-web-client-opening-book

for these web client changes.