WebSearch: fix detailed record page tab tracebacks

* Fixes tracebacks in certain detailed record page tabs
  (usage, files, etc).

* Fixes keywords tab that was not showing proper page body.

* Adds regression tests for each tab in order to prevent this error
  from happening again.

Reported-by: Fredrik Nygård Carlsen <me@frecar.no>
Reported-by: Ole Rønning <olerng@gmail.com>
Signed-off-by: Tibor Simko <tibor.simko@cern.ch>