[Subcorpus] Expand the ways of creating a sub-corpus

Summary

A sub-corpus must be able to be created in several ways:

• in a graph, from the contexts displayed after a (multiple) selection of terms
• in a term table, from the modal/popin contents after clicking on the eye icon of a term, author, etc.
• in a Map term list page, from a (multiple) selection of checkboxes (e.g. all documents linked to a map list of authors/institutions)
• in a documents page, from a keyword search (already done in #384 (closed))

(we can create associated issues to segment these different use cases)