Allow DeploymentConfig->map() to return values in standalone environment

Allow DeploymentConfig->map() to return values in standalone environment

This brings the standalone closer to the behaviour of other environments, except that it will continue to return null if there is nothing mapped (where other environments will throw). ->read continues to return null in standalone in every case. Note that standalone will now return a value if there's one mapped for any (*) - which is a minor breaking change to the behaviour of the standalone environment.