catch TypeResolverError in case a parent entity also implements ITree but is not the root entity (closes #1956066)

Which has been broken with cw 3.10 refactoring. This also fix and incoherent
display pb in the regular cases: when adding first comment, it wasn't not
displayed similarly right after the ajax call and after a page reload.

actually make comment section 3.10 compatible: this div is now handled by the layout, no need for match_kwargs, no more 'Component' added to domid

avoid empty div when no comments and no right to add comment. Remove spurious parameters from ajax place holder url.

cleanup/refactor/document comment form generation on the way