base: missing link tag fix

* Fixes issue with link tags to record files not being present
  on records page.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
tests: hidden tags test case

* Adds test case to ensure hidden tags are not present in export formats.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>