Reintroduce complex search filters

https://jira.usit.uio.no/browse/BOTTINT-267

The manual filter workaround was incomplete. This lead to assertion error when trying to look up an employee with multiple accounts, even when only one was active.

This change implements proper manual filtering for "single person" lookups.

This change also reintroduces the complex filters. Complex filters may be disabled via a configuration parameter.