Make Scoreboard & Team implement DataHolder

[ItsDoot]

Bringing the discussion from Discord to GitHub to keep track of it.

Scoreboard and Team would be much more useful for minigame-style plugins if they implemented DataHolder. This would in general remove the need for plugins to introduce their own replacements that practically clone their behavior.

This should be doable in API 8 as well as API 7, and discussion with gabizou makes it seem that they can be persisted too.

[Cybermaxke]

Persistence will only work for scoreboards that are tied to a World. Unless we also start persisting per player scoreboards.