Allow adding existing teams to an organization

[waldyrious]

According to the docs, it is only possible to add a team to an organization at the moment that the team is being created:

To add a team to an organization, check the box “This team belongs to an organization” when creating a new team.

(Emphasis mine).

It would be more convenient to allow adding an existing team to an organization, in case it wasn't created as such in the first place.