Add schemas to resources at resource_create time

resource_update is not handled yet.

This assumes that any newly created resource comes with a CSV file uploaded to
the FileStore.

Very little testing has been done so far.

* Add lib/csv.py with an infer_schema_from_csv_file() function based on
  pandas.
* Override resource_create with a wrapper function that calls our code to add
  in the schema after the resource has been created.
* Add code to get the path to a resource's file in the filestore, use it to
  infer the JSON Table Schema for the resource, save the schema in an extra
  field "schema" in the resource.

Also a couple of other tidying up changes in here.
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