Make sort lists update only when relevant data is changed

[luisa-beerboom]

Closes #2458

How it should work now upon update:

1. If items were deleted they should be removed from the list, immediate sub-items should gain expansion and visibility level of the removed parent, all sub-items should be moved left
2. If items are added they should be appended to the list
3. Other changes like name-changes will not affect the list in any way. (i.e. the sort view will also not update names while opened)

Notes for testing: Please especially check if

• Actual changes with the agenda item (for example change of topic title) still trigger an update
• Other sort lists are negatively/positively affected (for example the motion call list), as this performs changes in the base class

[emanuelschuetze]

Open agenda sort view > Collapse all items > now trigger autoupdate in an other tab:

• set done flag for agenda item => sort view expand!
• add new topic item => sort view expand!
• switch from public to internal => sort view expand!
• add/edit some agend details (e.g. duration, comment) => sort view expand!

Similar problem in motion call list: collabse all motions > change metadata (e.g. state) in an other tab => call list view expand!

[Elblinator]

code-review