[Messages] refacto with DataLoader + repair migrations

...igrations/20190511000809_create_messages_announcements.js

db/migrations/20190511004131_create_messages_answers.js

db/seeds/04_dummy_announcements.js

src/graphql/models/messageModel.ts

src/graphql/object_resolvers/groups/groups.ts

src/graphql/object_resolvers/messages.ts

src/graphql/object_resolvers/messages/announcements.ts

src/graphql/object_resolvers/messages/answers.ts

src/graphql/object_resolvers/messages/events.ts

src/graphql/object_resolvers/messages/messages.ts

src/graphql/object_resolvers/messages/privatePosts.ts

src/graphql/object_resolvers/messages/questions.ts

src/graphql/object_resolvers/requests.ts

src/graphql/object_resolvers/users.ts

src/graphql/resolvers.ts