Authors and Users in ELNs

Related to #910 (closed)

There already are two sections:

• nomad.datamodel.datamodel.Author (for human authors in general, first_name, last_name, email, affiliation)
• nomad.datamodel.datamodel.User (specialisation of Author for humans with a NOMAD account).

For User we should provide a specialized edit component that can be used for reference quantities that use User as type. This should for similar to what we have on the "manage users" functions on the upload page.

For Author we should provide the necessary ELN annotations that allows to use the section as a sub-section or base section in ELNs.