Allow to interact with the API from the reference docs

[odrotbohm]

As the API uses HAL as media type, it would be nice to have the HAL explorer (available as WebJAR) deployed with it and linked to from the reference documentation. Alternatively, CORS configuration could be defined so that the API can be interacted with from a publicly deployed HAL Explorer instance.

This would of course only allow browsing the reading endpoints, for starters. Also, HAL curies could be used to link to and transclude sections of the reference documentation in the browser itself, if link relations can be translated into pointers into the docs.

The server could also expose HAL FORMS templates for the state transitions that add and delete releases so that HAL Browser would present a UI for those and render the resulting JSON payload as preview.