- Remove all Roboto files

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

#513

- Can also be used with other elements

#512

- Remove dynamicPositioning from PositionProperties. This is not 
knowledge that the element needs to know. In the few places it was used, 
it was fixed or solved by asking the containing section about which 
positioning is active.

- Fix and improve cloze child sizing. All can now have dynamic width and 
height.

- Fix empty lines in ClozeDocument rendering

- Editor SelectionService now knows if a cloze child is selected. This 
way the PropertiesPanel can show valid dimension inputs regardless of 
the underlying section.

Also restructure files containing interfaces.

- When the height of the child elements of a cloze element is increased,
they all now grow out of their center

This was necessary because the new text selection action of the button
is not a navigation.

- Make position props on buttons optional
- Move UIElement creation back to Factory instead of within Section

Also add it to the likert row dialog.

#112

This way elements can handle their logic themselves without having to
rely on outside utility classes.

Also restructure files in common in a more logical way.