Gauss Sphinx Documentation

@gcorti @adavis @kreps @admorris the scaffold of the documentation is ready!

https://lhcb-gauss.docs.cern.ch/ will redirect automatically to https://lhcb-gauss.docs.cern.ch/Futurev5/index.html

to preview the version available on this MR you may visit: https://lhcb-gauss.docs.cern.ch/mimazure-gog-docs/

I will add more things, but the baseline should already go