- Make position props on buttons optional
- Move UIElement creation back to Factory instead of within Section

Use a horizontal aligned placeholder for dynamic aligned drop lists
when there is more than one element in the list

- Refactor variable of the placeholder dimensions

- Important for vertically positioned drop lists
- Analogous to the calculation of the height

- Replace pixel calculation with percentage values
- Use of only two modes: full fill or line

#343

i.e. something has been clicked.
Since the value is not used on the player, we also need to check the 
FormControl value.

#335

- This makes the behavior identical to real form elements
- To trigger the focusout event, the HTML element needs
the tabindex attribute

simple dropdown lists need a minimum height so they don't collapse
if they don't contain any element

Using disabled cause conflicts with reactive form in player

- Add "isOlderThan" method to the "SanitizationService" to distinguish
old ToggleButtons with the property "option" from new ones
- Use SanitizationService.isUnitDefinitionOutdated in Player to set
the unitDefinitionVersion (should be modified!)

Use css grid instead of flex plus calculating margins in template

Using the html property "disabled" results in a warning message in the
player when reactive forms are used at the same time.

Use the same settings as in simple drop list

ViewEncapsulation.None is required for overriding tooltip

DragNDropValueObject no longer has the stringValue property
but a TextLabel with text

Aslo create new props panel component and move border stylings to 
separate fieldset (wihtin the styling tab).

#291

One as a general label above the table and one for the first column 
heading.

Since this is no proper InputElement separate properties panel inputs 
are used.

#272

To be the same as with Material inputs.

#319

Add new parameter 'itemsPerRow'. This limits the grid columns used, 
making items move to the next row if overextending.

Also simplify component structure.

So TipTap does not moan about empty document.
Put placeholder text in the cloze document instead of the component 
template.