Draft: Official answers Add more flexible pdf rendering

Part of !429 Add more flexible pdf rendering (backend + frontend possibly) - or update pdf-js at least

Add ability to reference PDF (frontend-only)

• Modify/extend existing PDF renderer to enable 2d clipping instead of 1d like atm.
• Integrate custom OfficialAnswers component into ReactMarkdown.
• Create a simple parser for pagenumber and cords.
• Make it display a helpful error message if the syntax is wrong
• Figure out how to reference/get the official solution pdf
• Fix relative coordinates
• Handle invalid input in a good way. (Currently just an error in the console)
• Add correct scaling
• rename solution_file to solutionFile
• Add different pdf source support
• Fix re-rendering issue.