This may happen when changing the Clote document property.

Also move cloze-code into Cloze and no longer have it in a general 
purpose service.

This is done within the element's logic.

It now uses the page index the menu (that was used to delete) belongs 
to, instead of the selected page index.

- Image
- Hotspot-Image
- Audio
- Video
- Geometry
- DragNDropValueObject (imgFileName, audioFileName)
- LikertRowElement (imgFileName, audioFileName)

Also refactor a lot of stuff around the page canvas and unit view.

#684

New section components no longer get their number on creation. This has 
the effect that the section gets a new number and is updated again with 
all others after that.
Numbering of all sections is triggered in one place (UnitService) and 
updates all existing sections.

This would alles changing things that are deliberately left out in the 
props panel.

Connect all lists of that section.

Setting the mode in the constructor was too early.

Everybody is considered expert but role 'developer'. The host 
application allows not saving the unit when rights are insufficient, so 
the editor needs not to take care of that. Having full rights allows for 
better inspection of units even if it can't be changed(saved).

#669

This is only used by the Editor. It was in common while the 
SanitizationService was used by the Player which then could display 
errors. Sanitization has been refactored and this is no longer needed.

Separating code changes is rather hard right now, so there is a lot of stuff that is part of this commit that should not. Details below.

- All elements have static fields that holds their title and icon. This way dynamic lists can be built (for example for delete dialog) which show title and icon for all elements. ALso icons and names can be changed in one place.
- Template-Tab has been added. This should have templates to help creating groups of ui elements. This is work in progress and there are actually no templates yet. So this will change or even be removed in the future. This is mostly UI, the code is "TODO".
- Refactoring and improvement for delete and reference dialogs
- Delete logic refactored for elements, sections and pages. There are no longer different dialogs when references are found, but instead one dialog that can do both.

Visual overhaul and another way of inserting a section. The section code 
is saved to a global variable which can be used as well. Does obviously 
not work accress edit sessions or different units, therefore the old way 
is preserved.

Only works for a few commands (mainly page and section stuff).

- Adds new menu to page-bar, which shows issued change commands with a 
button to rollback the latest change.
- Added warning to the UI element that this is a experimental feature 
and can destroy units.
- Undo is done by having the normal function to apply the change to the 
unit-object and another to undo this change. The HistoryService manages 
the list and calling rollack (via UnitService).
- Further refactiring to the unit services.