renamed QueryStringFreeUri metric to QueryParamFreeUri
renamed QueryStringFreeUriTest test to QueryParamFreeUriTest
added query parameter-free URI metric to config
added DereferenceableForwardLinks metric skeleton and configured it
added prefix attribute to Metric interface and all classes

- updated interface
- added setter method
- added call of this setter method to provide the prefix information
- changed visibility of some other attributes
enabled and implemented DereferenceableForwardLinks metric