Feature: combine filter with collection query

[petschki]

We have the following scenario here:

• A customer created a collection which shows items of a specific Subject
• those items also have several other subjects assigned so we wanted to add a Subject filter to further narrow down the collection to those additional subjects.

This cannot be done right now, because the filter overrides the criteria of the collection query.

We're thinking about implementing a checkbox which says combine filter with collection query and handle it as AND combination. From the UI perspective it would also make sense to "hide" the selected collection query values in the filter list and only show the additional selectable values.