Create gource.io video for JabRef code

[Siedlerchr]

http://gource.io/

There is already a video which captures the dev up to 2015:
https://www.youtube.com/watch?v=WFXNmAKG6vA

Tips on how to create a video:
https://github.com/acaudwell/Gource/wiki/Videos

[koppor]

More recent gource: https://www.youtube.com/watch?v=cFuZnzq97sQ

[tobiasdiez]

That might be a valuable addition for the dev docs, but not for the main page. Thus let's close this.