(Tabular) Data Package Extension

Support for Data Package format (esp tabular data package) in CKAN

Specifically suggest API of:

```
GET /dataset/{name}/datapackage.json
POST /dataset/{name}/datapackage.json would also be nice but maybe action API would be better

e.g.

/api/action/datapackage_create => creates a dataset with resources as appropriate ...
```

Since datapackage is _very_ similar to CKAN dataset + resources should be straightforward. One major question is where we store the table schema for resources (I presume we just put this into resource extras ...)

No files or tests are named. Begin by reviewing CKAN's dataset and resource API alongside the Data Package format, then clarify the proposed GET and POST or action API and where resource table schemas should be stored; done means an agreed, implementable scope.

Written by the indexing model from the issue text.