* refac(#173): harmonize InvitationSent

* refac(#173): update metadata.scale + docs

* refac(#173): harmonize *MembershipAdded and *MembershipRemoved

* refac(#173): harmonize *CertAdded and *CertRemoved

* feat(#173): docstring for calls

* feat(#173): add SmithCertificationRemoved event

* feat(#173): rename CertificationReceived to SmithCertificationAdded