Support org-mode documents

Description

Org-mode is a very well known format in the scientific community.

It is very handy for note taking, project and knowledge management. Github supports org documents.

Proposal

Add full support of org format to properly render previews as well as use it for wiki pages.

Links / references

• https://en.wikipedia.org/wiki/Org-mode
• https://orgmode.org/
• https://github.com/orgzly/orgzly-android/blob/master/README.org