Extensive improvements to the Arrow Fight multiplayer example (#692)

- Added bots with randomized movements that only spawn while there is 1 player in the lobby.
- Now when players join a game that has bots in it, the bots will be removed and the players will play together immediately.
- Changed the way the pause "leave game" button works, now only the player who presses the button will exit the game.
- Removed the old drop out handling where players disconnecting would kick everyone from the game.
- Tweaked how the score messages are changed, now only the host changes the text. (Prevents conflicts between scores)
- Swapped out the level previously made with tiled sprites for a tilemap object instead.

Author: HelperWesley