[#52755771] Added source_class to HdfsDataset

The Allowy access control system was attempting to derive the Access
control class from an instance of HdfsDataset, but no such class
existed.
[#52755771] Fix statistics display of HdfsDataSet

The HdfsDataSet was not displaying correctly because the presenter
being used at render time didn't support its relevant attributes, that
being file_mask.

The DatasetStatistics#build_for method now instantiates a
HdfsDatasetStatistics for HdfsDatasets.