- Method is already defined in superclass

#583

#596

#596

Before it was just the bottom helper row.

#592

- New property group for flexible layout with more options to change the 
behaviour. It is now possible to build all other operations in this 
preset.

This is a free operation type that does not render much.

#590

#588

#588

Small cells and canBeCrossedOut are property of the row as they are all 
cells or none.
Additional property 'is2DigitHelperRow' is for different types of helper 
rows: single-digit in no crossing out or 2 digits with crossing out. 
2-digit is only for the top 2 substraction rows.

#589

This holds variable names, taken from the GeoGebra applet, and uses 
those variable values in the value. This makes result analysis easier.

#579

SInce this is a non-Material element the font is not automatically 
inherited. Needs to be done explicitly.

#574

- Minuend instead Subtrahend is strikable

#571

#578

#574

#560

style used in other cloze children causes the error
':host {display:flex !important; width: 100%; height: 100%;}'

#558

#559

The former solution was affecting the selection CSS of the button. Now 
the text is moved down instead.

#562

#542

This is much smaller and the intended way for web apps.

#457
#539

The directive for dynamic backgroudn color was outdated. Directive is 
removed and problem is solved via CSS custom variable.

#561

Gridsizes were accidentally changed from array to object.

The ClozeDocument was not cloned properly. Since it is possibly 
infinitely nested, manual reconstruction is less viable.