Fix alignment of Editable component #624
Description
The margins of the Editable component are used to center the component on the page at a max-width of 100ch while the text is justified-left. However, when the text is less than 100ch wide, the whole component becomes centered and the text no longer appears justified-left. This also means, it is hard to display another text component with a similar layout.
The layout of header and content of the Editable component should be changed such that it is independent of the text length of the content and such that the position on the page (centering) should be taken care of by the page rather than the component.
