~jaro/balkon

ref: 4ebfe390a1e8b16f42c6bdb51c135c895a7ce022 balkon/src/Data/Text/ParagraphLayout/Internal/Plain d---------
Refactor lineNumbers into a common module.
Refactor pagination to allow rich layout.
Separate interface-independent constants.
Add user data to spans.
Separate internal plain Paragraph/ParagraphLayout.