Updated docs to subscription endpoint change
Cleanup and PEP8's
docstrings
Moved admin subscription method to admin folder
base for user subscription method
Update subscription endpoints

* Change occurences of 'join' permissions to 'subscribe' everywhere
* Endpoint GET /people/username/subscriptions, now returns subscriptions directly, without user object wrap
    - updated related docs and tests
* Add unsubscribe permission when subscribing to a public context
* DOCS: Added description of subscribe permission
* TESTS: Added tests for plain user subscription
Add docs for plain user subcribe action
Update on subscriptions

* Move subscription-related tests to test_subcriptions.py
* Restrict GET /people/{username}/subscriptions to the current auth
* Update related docs and tests
Implement unsubscribe from a context

* As a admin and as a User
* Make context.removeUserSubscription accept an optional list of users to delete
* Tests and documentation
Listing of public contexts on GET /contexts/public

* Fix missing 'join' parameters, to 'subscribe'
* Update tests and docs