Endpoints to manage datasets

Refs https://redmine.teklia.com/issues/3653

We need a few new endpoints (in category dataset) to manage the brand new datasets:

• ListCorpusDataset must provide a paginated list of all datasets in a given corpus
  • accessible to corpus guest, contributors and admins
  • output fields: id, name, description, state
• CreateDataset must allow a corpus contributor or admin to create a new dataset
  • input fields: name, description, sets
  • output fields: same + ID
  • state is always open upon creation
  • creator us current user
• UpdateDataset must allow a corpus contributor or admin to edit an existing dataset
  • input fields: name, description, sets, state
  • ⚠ state is only modifiable by a ponos task (which uses that dataset, if you are after #1517 (closed))
• DeleteDataset must allow a corpus admin to delete an existing dataset, only if the dataset state is open