/team command + Concept

I think we need the /team command and the way to use it as a target selector to Minecraft.

How it works:

    -Each entity/player has a team value that stores its team. It is only valid if the team has been created before. This value is stored along with all other nbt-values (wich means that a entities/players team can be edited with a nbt-editor). If the entity/player has never joined a team the value stores no value. If multiple entities/players have the same value they are automatically in the same team.

    -a team has to be created before a entity/player joins it: /team create <teamname>

(for example: /team create Team1)

    -each team has a max. size of members and a criteria that determinines the type of entities that can join: /team setting <team> <entityType|TeamSize> set <EntityType|int> (for example: "/team setting Team1 entityType set @e[type=!sheep]" or "/team setting TeamSize set 10" )

    -an entity/player can try to join a team: /team join <team> <target> (for example: /team join Team1 Steve)

    -making a player/entity leave their team: /team leave <target>

    -listing the members of a team: /team list <team> (for example: "/team list Team1")

    -teams can be used as target selectors (for example: "/give @a[team=Team1] diamond" or "/kill @e[team!=enemies]")