Provide sufficient context to check 'delete' permission in AjaxEditRelationCtxComponent
Call rdef.check only when both fromeid and toeid are available. Though only
call it once (for the first encountered related entity).
Factorize a bit to keep handling of CSS/JS addition the same.
Closes #3670209.
What's new in CubicWeb 3.20
===========================
Deprecated Code Drops
----------------------
* most of 3.10 and 3.11 backward compat is gone; this includes:
- CtxComponent.box_action() and CtxComponent.build_link()
- cubicweb.devtools.htmlparser.XMLDemotingValidator
- various methods and properties on Entities, replaced by cw_edited and cw_attr_cache
- 'commit_event' method on hooks, replaced by 'postcommit_event'
- server.hook.set_operation(), replaced by Operation.get_instance(...).add_data()
- View.div_id(), View.div_class() and View.create_url()
- `*VComponent` classes
- in forms, Field.value() and Field.help() must take the form and the field itself as arguments
- form.render() must get `w` as a named argument, and renderer.render() must take `w` as first argument
- in breadcrumbs, the optional `recurs` argument must be a set, not False
- cubicweb.web.views.idownloadable.{download_box,IDownloadableLineView}
- primary views no longer have `render_entity_summary` and `summary` methods
- WFHistoryVComponent's `cell_call` method is replaced by `render_body`
- cubicweb.dataimport.ObjectStore.add(), replaced by create_entity
- ManageView.{folders,display_folders}