Add automatic BibTeX reference creation (BB-14640)

In order to create BibTeX (.bib file) entry citing certain commits in Git Repository.
This could be deduced to a more general view:
Consider a text file with placeholder (like <<COMMIT>>) which would be automatically replaced with the commit number, when showing or downloading this file and <<LINK>> which would be automatically replaced with the link of the source files for this commit. (This is for a fixed commit, not the last commit and not the commit of this text file itself.)