Mass Category filtering lists objects from sub-tree

This FR builds on the vision laid out in Category for Huge Amount of Data. 
This project depends on / requires that the following list of PR and FR is accepted and implemented 

• Pull Request UI Filters (Implementation)
• Pull Request UI Filters
• Filter-Configuration in Categories

1 Initial Problem

Filters above lists in categories only filters what is on the list and not what is encompassed in containers in the list.

2 Conceptual Summary

Users are to include subtrees in filtering. 

3 User Interface Modifications

3.1 List of Affected Views

• Filters in Categories

3.2 User Interface Details

3.3 New User Interface Concepts

None.

4 Technical Information

Killing, Alexander [alex], 16 May 2019: Large subtrees may reduce performance. We should add an information text adressing this.

5 Contact

• Author of the Request: Tödt, Alexandra [atoedt]
• Maintainer: {Please add your name before applying for an initial workshop or a Jour Fixe meeting.}
• Implementation of the feature is done by: {The maintainer must add the name of the implementing developer.}

6 Funding

If you are interest in funding this feature, please add your name and institution to this list.

• …

7 Discussion

Killing, Alexander [alex], 16 May 2019: I support the idea. We should add a performance information text (see technical issues).

Kunkel, Matthias [mkunkel], 16 MAY 2019 : I would use "Filter Behaviour" as section title instead of "Sub-Categories". Or do you expect a lot of additional sub-category related settings in the future?

Tödt, Alexandra [atoedt] Comment of Matthias is now reflected by mock-ups

JourFixe, ILIAS [jourfixe], 20 MAY 2019: We highly appreciate this suggestion and re-schedule the feature for 6.0.

8 Implementation

{The maintainer has to give a description of the final implementation and add screenshots if possible.}

Test Cases

Test cases completed at {date} by {user}

• {Test case number linked to Testrail} : {test case title}

Approval

Approved at {date} by {user}.