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

The directive for dynamic backgroudn color was outdated.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

#561

#449

- position
- label
- icon

Was completely broken: not showing at all in Editor, not clickable in 
Player.

Removed pipe 'aspectInputBackgroundColor'. Replaced by more elegant 
solution via inherited background-color.

THis component was still somewhat broken after the Material update.

#541

#545

The inclusion of svg icons via the src parameter of an image tag
is prohibited in the test centre for security reasons

- Remove all Roboto files

Since there is just one font, this setting can be safely ignored. This 
is easier than sanitizing all elements.

#513

#499
- Problem was due to changes in the latest minor material update

#533
- Remove unnecessary and wrong setting of underline property

#531

#532
- Replace the global label identifier

#535

#454
- does not work in FF

#456

- Add Property "hasAutoHeight"
- Add Directive AutoHeight

#520

Make player control bar inherit pointer-event styling. This way the 
Editor can set it to none, while acting normal in the Player.

#524

- Don't report empty reference string as invalid
- Add VideoElements to check