These endpoints usually gives access to the "latest" object version
which is not clear.

If this is really something we want to provide it should be using
an explicit route ending for example with "latest" at the end.

This will make the code cleaner and allow to do custom
error handling properly.

The items needed are the same as provided by the fullname method.
This allows to integrate the Experiment creation serializer

Some code still uses it in other parts so make it easier to re-use.

Also move all imports at the top, it's counter-productive
to have try/except import clauses on a package that is
mandatory for the code to work.

Fix supervision lists expand

Closes #549

See merge request !329

Fixes #549

Fix object existence check in common serialiser

See merge request !326

The check worked with SQLite but not with PostgreSQL.
In any case, since we have a user object here, there's no
reason to not use it directly.