Add reference property to reports

[xsist10]

To take advantage of #4, a reference property should be added to the Check class and used to store the appropriate external reference link. This link should be displayed on all output formats.

• Add getReferenceUri function to the Check interface
• Create getReferenceUri function in each check that has a wiki reference and mark it return the URI of the reference.
  • If no page is created yet, return empty string