Now manages it's width and height itself.

Also has some new properties:
- verticalOrientation should be self-explanatory
- dynamicWidth allows the user to set a width manually. The buttons on 
the element automatically stretch to meet the set width (or height).

Cloze elements are displayed inline and have no way to show a label.

- Explicitly set the value of the form control of CompoundChildren,
because they are not yet fully registered in the onInit phase.
- Use ChangeDetectorRef to prevent
ExpressionChangedAfterItHasBeenCheckedError

Now correctly sets the chosen background color and additionally sets 
another (configurable) color to the selected value.

This is meant solely as a cloze child as a representation of a radio 
button functionality.