Extract 'admins' api to be independent from pouchdb plugin

[minrwhite]

As detailed here in the "Out of scope" section, there are better ways of organizing this module. This issue is to define the scope to encapsulate this work.

Tasks:

• [ ] extract the api to be exported as a module directly, rather than to be attached to pouchdb.
• [ ] rename the repository - currently open to suggestion - maybe hoodiehq/admins would suffice?
• [ ] deprecate the current pouchdb-admins npm module
• [ ] republish to npm under new name - again maybe @hoodie/admins
• [ ] update consuming hoodiehq projects to use the api

[minrwhite]

Note: This seemed to be interrelated to the work that @g2rm is doing in hoodiehq/hoodie-server#526

[gr2m]

I think I would rename this package to couchdb-admins, as it mimic CouchDB’s admins APIs, and remove the pouchdb plugin implementation.

I don’t think we will use this package in future for hoodie core, I think we will store admins the same way we store user accounts, either in the same database with a admin role or in a separate database, it will make our lives much easier, and we no longer need to mimic CouchDB’s config API for admins