In fact, make changes in common to let the player understand the slider component.

It needs row and column to work. (It is using flex in the background.)

Use 'horizontal' and 'vertical'. Which are better terms and also align 
with other element's values.

Also improve conditional border style. The additional dragPreview is 
needed so the dragged item does not have the border.

This element has a list of string as editable options. Those strings 
form draggable elements which may be reordered or moved between 
different DropList elements.

Also refactor option change logic to allow any property not just the 
text property.

Now correctly shows a dropdown instead of a text area.

When selecting the preset value, sometimes the string is empty and it is 
not possible to differentiate the options. Therefore an index is added 
making it possible to reliably select a value.

This function will be implemented differently.

To not have the same name as likert rows and cause issues on the props 
panel.

This is necessary to reset elements like radio button group. We use null 
for that instead of undefined.

The check was in place before to make sure input fields only accept 
valid values (no text in a number field for example). Angular thinks a 
null value is valid so we have to do this extra check. This is now done 
directly in the template before calling the updateModel method.

Put the buttons to the right side instead of in the middle somewhere.

This makes it so that other options appear with strikethrough when one 
is selected.

This allows for further marking options on the text, which may be used 
for different purposes.

For elements which don't have this functionality the workaround is to 
use pointer events and make the elements unclickable.

Useful for longer text in textareas and does not hurt short text 
elements (like text-field).

This way the vertical size can be controlled.

The labels are still the internal names. Needs to be fixed next.

Also add corresponding UnitService methods.

The main components are right at top level and the directories below
mimic the data structure (unit->page->section).
The toolbar is only used in dev mode and does not belong directly to the
unit view.
The TextEditor is a complex component and deserves it's own directory
even though it is used within the unit-view. Might be refactored to its
own module later.

This is now only one field with string value. Unset is put by using 
'none', since mat-select inputs cannot deal properly with null values.