- 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

Octal characters are deprecated and don't work anymore. This solution 
uses an empty string over the whole line.

#502

The extension is needed to define text areas in the rich text editor
and make them available for the button component

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.