"Upload to..." impossible in containers of type other than 'Folder'

[sauzher]

Bring here this: https://community.plone.org/t/tinymce-upload-file-to-containers-other-than-folder-large-plone-folder-plone-site-impossible/16135/2

The problem is that selectableTypes are defaulted to ['Folder'] here

mockup/src/pat/upload/upload.js

Line 49 in c31dcf0

selectableTypes: ["Folder"],

IMHO, it would be nice either of this two options:

1. let the used related items pattern look for some generalist interface like IPrincipiaFolderish as suggested by @petschki (https://community.plone.org/t/tinymce-upload-file-to-containers-other-than-folder-large-plone-folder-plone-site-impossible/16135/3?u=sauzher)
2. get selectableTypes be parametrized so that a consumer (for ex. TinyMCE template) could pass its specific configuration via data-pat-upload. Actually TinyMCE has Products.CMFPlone.interfaces.controlpanel.ITinyMCESchema.plone.contains_objects configuration registry option that seems to fit quite well.