Improve video embedding

The current way of video embedding (via absolute path) does not allow to preview videos if you are adding videos on a feature branch. Make it possible somehow!

created branch 353-improve-video-embedding to address this issue

created branch 353-improve-video-embedding-2 to address this issue

mentioned in merge request !627 (closed)

mentioned in merge request !629 (merged)

mentioned in commit 66697448

closed with merge request !629 (merged)