Directory App: filters should be adaptive

[dtroelofsprins]

In the initial version of the Directory App adaptive filtering was included, however it turned out that it was not working properly (or not). It was therefore turned off (#3343).

This issue requests to include the adaptive filtering in the Directory App again:
Specifications:

• All options should remain visible (and selectable) in the first filter
• The filter options in any subsequent filters that are not in the search results anymore should be excluded from the lookup list.
• (Initially not available filter options should be excluded beforehand?!?)