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>