Implemented the concept of datasets. Datasets allow the space users to organize their data into collections with desired granularity. A file or directory marked as a dataset offers additional features, such as optional data and metadata protection or the ability to create persistent snapshots of the physical dataset contents. In case of a directory, a dataset covers all its subdirectories and files. Datasets can be nested, allowing users to compose arbitrary hierarchical structures. Added corresponding views for managing datasets and write protection flags in file browser Web GUI and a REST API, accessible under `/datasets`, `/datasets/{DatasetId}` and `/data/{FileId}/dataset/summary` paths.