nb: the routes are not changing as part of this, only file paths and
blueprint names.
invite -> service_invite
this blueprint handles fetching invites for a service, creating invites,
etc.
accept_invite -> global_invite
this blueprint handles accepting invites for now, but will also involve
retrieving service/org user invite data without knowing the service/org
id associated. i'm not in love with this name and open to suggestions,
but i wanted to contrast it from service_invite and
organisation/invite_rest.py.
