Normal user useless in database

[AlexandreDubray]

The only purpose of the current database is to store users that have special right. In our case, with SAML2 we do not need to store normal user (~700 users this year, could be the same or more each year). We could split the current database into a table for "normal" user table (empty in our case, but other use case might need it) and a "special" user table.

We also need to think how special user are added in the database

[francoismichel]

As this issue is more related to a special use-case of ours, what we will do is enable the use of non-SQLite databases and nothing else for the moment.