Fix/various bugs on textilizable block

This fixes three bugs:
* https://www.openproject.org/work_packages/15523
* https://www.openproject.org/work_packages/15582
* https://www.openproject.org/work_packages/15583

For the fix of the last (no more unnecessary warning wenn pressing the save button) I changed the layout as well so that it works more like the rest of the application.