Play support PUT & DELETE :key/enabled

In order to provide feature-switching in the [Workflow](https://github.com/guardian/workflow) app written using the Play framework, this PR implements Play controller with Actions matching endpoints that exist in the current Scalatra implementation.

Dependent on: 

- https://github.com/guardian/feature-switching/pull/6#

This PR implements actions only for:

- PUT /api/features/switches/:key/enabled
- DELETE /api/features/switches/:key/enabled

Further PRs will follow to add remaining endpoints.