[v9r3] Add documentation

About LogSE, Sandbox store, and create an index.html that makes sense. @zmathe would you please check that what is in the Certification folder still makes sense ? @fstagni I have the feeling that the dev folder could be trashed

I will try to understand as well why we have no index generated (https://lhcb-dirac.readthedocs.io/en/latest/genindex.html vs https://dirac.readthedocs.io/en/latest/genindex.html), and I would like that we also get proper code documentation. I will take care of this little by little