Modification de la db pour avoir plusieurs auteurs et recipients

.gitignore

...igrations/20181110192012_create_messages_announcements.js

db/migrations/20181110192431_create_messages_events.js

...ions/20190310155826_create_events_participating_groups.js

...tions/20190310155843_create_events_participating_users.js

db/seeds/04_dummy_announcements.js

db/seeds/05_dummy_events.js

db/seeds/07_dummy_requests.js

src/graphql/models/messageModel.ts

src/graphql/resolvers.ts