Test users support in the API

[andreskytt]

As a developer, I want to be able to explicitly tell the API that what I am doing now is for testing purposes and should follow a different path of business logic. By default, that path is probably "have no consequence whatsoever" but more complex interactions might, for example, redirect the calls to different instances running on a separate test environment

[andreskytt]

As a sysadmin I want to be able to flick the API between three different modes:

• Record. The (selected)inputs are hashed and the entire response is stored along with that hash
• Playback. If the input hash matches one of the recorded responses, the recorded response is played back without any business logic being executed
• Normal. Neither playback nor recording happens