make all fields in frontend sortable

[kaggl]

The following fields are used in the frontend search table right now:

courts: "name", "main_owner.name", "start", "end", "kategorie"
events: "name", "start", "end", "kind" (there may be more coming eventually)
institutions: "name", "start", "end"
persons: "name", "first_name", "alternativenames", "functions", "institutions"
places: "name", "kind"
realtions: "source_kind", "source.name", "relation_type", "target.name", "target_kind"

these fields should all be sortable

additionally, alle "ampel" fields should be sortable too