Support gameplay without bots

[CloneWith]

:warning: Is your feature request related to a problem? Please describe

Due to the nature of Halma, which is originally several players surround a board and play, this should be appropriate.

:bulb: Describe the solution you'd like

We can allow the bot number to be zero. Adding a bots switch could be helpful too.

:raising_hand: Do you want to develop this feature yourself?

• [x] Yes