Added more fields on dataset and added creative-work type

[xmnlab]

Example of graphql query:

# Write your query or mutation here
query {
  datasets {
    id
    author {
      id
      name
    }
    copyrightHolder {
      id
      name
    }
    copyrightYear
    creator {
      id
      name
      affiliation {
        id
        name
      }
    }
    dateCreated
    dateModified
    datePublished
    exampleOfWork {
      id
      name
    }
    license
    provider {
      id
      name
    }
    publisher {
      id
      name
    }
    url
  }
}

[xmnlab]

Example of mutation:

mutation {
  addDataset(
    author: {id: "person/1"},
    copyrightHolder: {id: "person/1"},
    copyrightYear: 2019,
    creator: {id: "person/1"},
    dateCreated: "2015-10-13T13:00:00Z",
    dateModified: "2015-10-13T13:00:00Z",
    datePublished: "2015-10-13T13:00:00Z",
    exampleOfWork: {id: "creative_work/1"},
    license: "https://opensource.org/licenses/BSD-3-Clause",
    name: "dataset2",
    provider: {id: "organization/1"},
    publisher: {id: "organization/1"},
    url: "localhost"
  ) {
    message
    success
    result {
      id
      author {
        id
        name
      }
      copyrightHolder {
        id
        name
      }
      copyrightYear
      creator {
        id
        name
        affiliation {
          id
          name
        }
      }
      dateCreated
      dateModified
      datePublished
      exampleOfWork {
        id
        name
      }
      license
      provider {
        id
        name
      }
      publisher {
        id
        name
      }
      url
    }
  }
}