Clear set scopes for Astropy products

Two ideas were floated around:

* Chart to group them into "actively being developed", "bug fix only", and so on.
* A dashboard like [Astropy Project Dashboard](http://www.astropy.org/astropy-dashboard/status.html) that displays similar info as above, but it scraps the info from some special repo metadata (repo topics or a special JSON/YAML file at root dir).

Once set, the scopes should be communicated clearly to the rest of the Astropy community.

Also related: astropy/package-template#497

Start by reviewing the Astropy Project Dashboard linked in the issue and the related astropy/package-template#497 discussion. Define the product-scope categories and decide whether their source should be repository topics or a root JSON/YAML file; done means the scopes are agreed, displayed consistently, and clearly communicated to the Astropy community.

Written by the indexing model from the issue text.