Add planning sessions

[antonkomarev]

Right now Game entity is what should be renamed to Session. And Game should become container of the Sessions.

There might be only one active Game in one Chat.

• Game start
• Game session attach
• Game end
• Game statistics

Planning Game Start

Command /game {game_name} starts game with provided name.

When game is starting, Bot sends a message:

Planning poker started: {game_name}

If {game_name} is empty — default name is (no game name).

If there is active game Bot should say that Game already started and you can't start a new one unless it's ended.

Planning Game Process

If Game in Chat is active — all Sessions will have game_id related to active Game.

If source message text is edited active Game message should be renamed as well.

• Update system message text on editing facilitator message text #38

Planning Game End

Command /game_end ends currently started Game.

When Game ends — Bot sends statistics:

• Planning poker ended: {game_name}
• Estimated topics count: {estimated_topics_count}
• Canceled discussions count: {canceled_topics_count} (if count > 0)
  • Cancel session on discussion phase #16

Message should be sent with disable_web_page_preview=True.