control: quotas for organizations
limits.max_orgs_per_user caps the organizations an account creates, counted by orgs.created_by (backfilled from the first admin). Membership in someone else's org does not count. limits.max_repos_per_org and max_bytes_per_org cap each org the way the per-user limits cap an account: repo create, fork, import, transfer, push, commit-file and apply-suggestion. admin org limits sets per-org overrides; admin user limits takes --orgs.
repo transfer now applies the receiving owner's caps, user or org.
Closes #325