Kick and ban from lobby

[UncleVasya]

Some banned players intentionally join lobbies to trashtalk people, so !tk command is not enough.

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• [x] add Player.banned_from_lobby flag;
• [x] add !lobbykick (!lk) command. It should set the flag too.

Or use another approach:

• use one "banned" flag, but let it have different levels: [NOT_BANNED: 0, BANNED_FROM_PLAYING: 1, BANNED_FROM_LOBBY: 2]

[UncleVasya]

Done.