Implement synchronized start games

[sei-bstein]

Enable Gameboard to structure games that require multiple teams playing the same game to "ready up" before allowing anyone to start.

Requirements

• Add a flag to Game which marks it as one which requires a synchronized start
• No player is allowed to click "Start Session" unless all players have readied and all teams have the minimum number of players specified by the game rules
• Once the session has started, any unenrollments/session restarts do not affect the game's availability to other players or teams.

Potential use cases

• Competition
• Shared educational sessions with Gameboard at the heart

[sei-bstein]

Implementation ideas

• Toggle on a board in admin
• Requires the approximate scheduling of a sync session (so we can define an entity that represents the group game/challenges)
• May allow admin to affiliate users with the sync session
• For this sync session:
  • shared challenge resources are only created once
  • Session timers are shared

[sei-bstein]

Resolved in 3.12.0.