Bump gds-api-adapters to 14.11.0

This adds support to the Panopticon adapter for the new tag endpoints
Add tag presenters

This adds two new presenters: TagPresenter, used to render a Tag 
instance in the required format for Panopticon, and 
MainstreamBrowsePagePresenter, which subclasses TagPresenter to override
the 'tag_type' attribute.

I've separated these concerns at this early stage as I expect there soon
to be a TopicPresenter which will also subclass the TagPresenter, but
which may include additional functionality that is currently provided
by the SectorPresenter.
Add a notifier for Panopticon

This adds a new class which encapsulates behaviour to notify Panopticon
when a tag is created, given an instance of a class that conforms to the
TagPresenter interface.

This also defines the Panopticon service, and provides an instance of
the service in development. A bearer token is always required when 
making requests to Panopticon using the API client. In development,
no assertions are made against the validity of the bearer token, as long
as there is a string present. (see the mock_bearer_token strategy in
GDS:SSO for more details)
Notify Panopticon when a browse page is created

This changes the MainstreamBrowsePagesController so that, when a browse
page is created in this app, a request is made to Panopticon to create
the browse page there too.

The notifier is invoked as part of the create action, and will fail 
noisily if the request is unsuccessful, as the Panopticon API adapter
will raise an exception. For now, it makes sense not to catch this, as 
consistency between this app and Panopticon is the most important thing.