Feature request for Bookmark/Sectioning & Iframe support

[Shnku]

Rnote makes modern note taking more easier on Linux. (xournal/xournal++ is classic), I am very thankful to this project.
from my side i think these features would be very use, also useful for enthusiasts .

• Bookmark or like markdown section, subsection, It will be helpful to jump to a note cause thats a bad habit of writing notes infinite long in both horizontal & vertical direction 😶‍🌫️ .
  The linking feature is something like that but is links the documents(and it is another good feature , onenote support this kind of linking)

• Another Idea i wanna talking about Iframe feature, then it will be possible to embedded some web reference and YouTube videos in place ... helpful for students like me.

Again Thanks in Advance

[Doublonmousse]

See #294 for the first point

For the second, see #911 and #913 (tldr adding html links is probably fine, but going further and it becomes a little more unlikely to be implemented, so that exporting to pdf/svg makes sense)