Currently, the share modal is always updated completly when:

* Adding a user (also when Begin of the insertionre-addingEnd of the insertion Begin of the deletion readdingEnd of the deletion a user with a different role via the autocompleter)
* Changing a user's roles
* Removing a user

This is to be changed so that Begin of the insertiononEnd of the insertion Begin of the deletion on End of the deletion

* Adding a user (also when Begin of the insertionre-addingEnd of the insertion Begin of the deletion readdingEnd of the deletion a user with a different role via the autocompleter)
* Removing a user

only the row within the list of shared with users is added/removed.

This should keep the focus where it is and avoid reloading the autocompleter after every action.