Improve bookmark data for PDF files

[BPerlakiH]

Following up the issue of #826
We might consider using more data from the PDF files for the purpose of creating bookmarks.
The following fields are displayed from Bookmarks:

• title
• (optional) short snippet
• (optional) image url

[kelson42]

At this stage my question is: Is that a good idea at all to have an image and a snippet extracted from the article? Do we really need that? Are we aware that such a requirement might a serious impact in term of code complexity to be done properly (next question would be the support of a Video file for example)?

[BPerlakiH]

@kelson42 I have created a proposition and a draft PR, to help you with this question: #830

[BPerlakiH]

I think it can be now closed, as the bookmark PR is merged.