Make use of Parsr's heading detection

[bogdankostic]

Describe the solution you'd like Parsr has built-in heading detection. We should make use of it and add headline information of PDFs to the converted Documents. As far as I know, Parsr only detects the headings but not the hierarchy of the headings. We might determine the hierarchy of the headings by using a heuristic based on the font size of the headings.