support for data packages with example

There is a new datasets.csv file and support for data packages. Changes
include:

 - All values are now sequences.
 - Data packages are integrated as "Subcategories"
 - There is support for OPeNDAP data.
added enable column

The Enable column allows dataset to be turned on and off.
new dataset file with packages

This new dataset file has some data packages in it.
Merge branch 'master' into issue-12-packages
Changes to read the new format of ocgis_datasets.json
Refactoring ocg.py
Upgrading dataset validation in the web interface.