#61068020 Added SurveyInvitationRequest model, with basic aasm behavior
Remove unused, duplicate relation
Say an invitation request is pending before it is accepted or declined, so we don't trip up on multiple uses of 'request'
#61068020 Create an invitation when a request is accepted and send notification.
Also keep a reference to the request on the invitation.
#61068020 Added SurveyInvitationRequestsController with create accept and decline routes.
Added unstyled, placeholder view work for creating a request from a survey invite, and accepting/declining from the survey moderator summary view.