Gallery for entity references via JS

Problem/Motivation

If you have nodes with referenced entities you are not able to group the galleries by node - especially if you have multiple node with multiple images on one page (like view results). In #2957030 the approach is to place the colorbox one level above in the referencing entity. This did not work for us so we choose the more easier war to aggregate the gallery by javascript.

Steps to reproduce

- Create a content-type with an entity-referenced media entity (multi-valued)
- Cretae a node with this content type and add more images than one.
- In the colorbox-settings youcan not choose the right gallery type because the node id is unknown while generating the colorboxes.

Proposed resolution

Use this patch.

Remaining tasks

Add more flexibility (e.g. options for "media entity" or "taxonomy term" as parent and a option for "1st parent" or "2nd parent").

User interface changes

Add a new gallery type "Parent node (via JS)"

API changes

nonde.

Data model changes

none