Add more layers of tree nodes

[jeanpaulrsoucy]

Add two more layers of tree nodes:

First, add an additional set of nodes within each province/territory node for each "meta_group_2".

Second, add a set of nodes (under the appropriate node---either "meta_group_2" or "meta_group_1" directly) for each "meta_url"---and finally put the actual dataset nodes under these so they are grouped correctly.

The purpose of this is to mirror all of the functionality of the current README-based dataset list so that it can be made redundant and eliminated.