Make this dataset valid DDF dataset

For now this dataset is not valid ddf dataset yet: measure/unit/tag is not DDF collections, right?

To make this dataset valid ddf dataset, I suggest:

- change ddf--measures to ddf--concepts--continuous
- change ddf--tags and ddf--units to ddf--entities--tag and ddf--entities--unit
- add ddf--concepts--discrete for all discrete concepts in this dataset

What do you think?