Organization create changeset should fulfill associated OrganizationInvite

[begedin]

Policy.Organization enhancement in #1230 deals with allowing the creation of an Organization via invite.

However, the changeset we use to perform the creation needs to be able to fulfil the invite.

• add code virtual attribute to organization
• make the create_changeset cast this token
• add a prepare_changes step to create_changeset, which sets OrganizationInvite to fulfilled: true

Estimates

~ 1 hour