~jaro/balkon

ref: 0975c99f8e8fc2f33c968daa8968444bb0c026c5 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.