Fix null pointer exception when @XmlIDREF was used incorrectly

Change-Id: I321b24f31176e394fb1764a68ae1680199cc9e43
Tested-by: Mr. Jenkins
Reviewed-by: Tomek Piotrowski <tomek.piotrowski@atteo.com>
Scoped ID resolver was failing on any not unique ID

Non-unique IDs are permitted. Only when referenced the ID should be unique
in the scope of the expected class.

Change-Id: I2eeafbba6a6e74e8b5b84458b1a59620b816c76f
Reviewed-on: https://pirx.atteo.com/gerrit/214
Tested-by: Mr. Jenkins
Reviewed-by: Tomek Piotrowski <tomek.piotrowski@atteo.com>
Add toString method to Configurable

Change-Id: Ibc5196e05f764d11b467de69e3000ab989cc89af
Reviewed-on: https://pirx.atteo.com/gerrit/215
Tested-by: Mr. Jenkins
Reviewed-by: Tomek Piotrowski <tomek.piotrowski@atteo.com>