refactor viewers autoload

[Drathal]

closes #71 prepares #59

• refactored autoload/viewers.gd
• !join and !leave are handled for all games automatically
• it now holds a list of waiting viewers
• emits an event whenever a viewer is added / removed from the viewers list
• when a user leaves chat, that user is also removed from the viewers list
• the viewers list can be locked / unlocked
  • when locked viewers are added to the waiting list
  • when unlocked the waiting viewers are added to the viewers list and a event for each user is send
• refactored all games to work like before
• refactored pool_royale to take advantage of the events (less code)
• the !join bug should be gone

I tested it but it would be great if we can test that also with real viewers

[MrEliptik]

There's a bug in get_players_count(), it's not returning the right amount of players.

[Drathal]

It now also handles dead viewers.