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.

#449

- position
- label
- icon

- Replace throwing Errors with InstantiationErors in unit, page and
  section in strictInstantiation mode

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

The CSS selector for what the element to color changed (most likely with 
the Angular Material update). Also a lower z-index is needed to not 
cover the text.

#534

- 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

#506

The individual rows are considered as a whole and are therefore
adjustable as a whole via the parent element

#454
- does not work in FF

#461
- This property will be used for all input assistance presets
  in the future

#456

- Add Property "hasAutoHeight"
- Add Directive AutoHeight

#520

#506

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

#524

#452

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

Absolute position didn't work if the display scaling factor of the
operating system or browser is not 1.

#511

GGB elements without toolbar aren't loaded, if this parameter is true

#511

- crossOutChecked adds line-through styling if checked. This is used in 
Cloze texts to cross out words.
- This means Checkbox is no longer a PositionedElement and does not 
validate PositionProperties

This way the unit definition version is set to current if an old version 
is detected (by the Editor).