To be done in this issue:
  - Increase threshold for batch deletion to 5000 segments (if less segments are deleted one by one, otherwise old batch deletion is used)
  - Add message about blocked UI
  - Stop search when delete all button is clicked (currently search is not stopped which adds load on the memory while deletion is happening)

Message text:

EN: Each segment of the current search will be deleted individually, which may take some time. The UI will be blocked until the process is complete. If you wish to use TM-Maintenance during this time, please open a new tab.

DE: Jedes Segment der aktuellen Suche wird einzeln gelöscht, was einige Zeit dauern kann. Die Benutzeroberfläche wird blockiert, bis der Vorgang abgeschlossen ist. Wenn Sie TM-Maintenance während dieser Zeit nutzen möchten, öffnen Sie bitte einen neuen Tab.