Documentation include "user images"

[WalterMoar]

The documentation in the Wiki allowed editors to paste images from screenshots, etc. This resulted in the images being uploaded to https://user-images.githubusercontent.com. We need to move all these images in this repo.

Definition of Done:

• [x] Come up with a logical naming convention / filesystem structure for images and add it to the Style Guide
• [x] All images in the documentation are stored in /docs/images, possibly within a tree file structure
• [x] Check for any other content (other than YouTube videos) that may be hosted outside the documentation

[vijaivir]

The images and videos have been migrated.