New name: richTextOptions

Unit definition version has been raised accordingly.

verticalButtonAlignment is the new property for likert rows, which tells 
the actual radio button to either be at the top or in the middle.

Instead, use :host in conjunction with ::deep

- Use fixedSize always together with dynamicPositioning!
- Rename css class 'center-content' to 'fixed-size-element'
'fixed-size-element' ensures that the content does not overflow.

The previous solution, which uses a top position of 50%, did not work on
iPad

- This improves scroll snap behaviour
- Set background color of page
- Interpret the margin of a page as padding. What it really is