Add side-bar box for record uploaders

Closes #42 (closed)

This MR adds a box on the right side below the "export" box, which lists the uploaders:

Note that the current implementation only displays the box if the record exposes the record.parent.access field, which is only dumped if the active user has "manage" permissions on the record: https://github.com/inveniosoftware/invenio-rdm-records/blob/master/invenio_rdm_records/services/schemas/parent/__init__.py#L26
Effectively this means that the user has to be logged in and either be an admin, or one of the record owners.